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Jan. 20, 1942. C. J. KINZE ET AL Re. 22,011 METHOD OF MAKING ENAMELYNARE Original Filled Nov. lo, l938 2 Sheets-Sheet l

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Reissued Jan. 20, 1942 Re. 22,011 UNITED STATES PATENT OFFICE 22,011 METHoo of MARINGENAMELWARE Charles J. Kinzie and Charles E. Commons, Jr., Niagara Falls, N.Y., assignors to The Alloy Manufacturing Company, New York, N.Y., a corporation of Maine Original No. 2,249,007, dated July 15, 1941, Serial No. 239,772, November 10, 1938. Application for reissue October 22, 1941, Serial No. 416,134 19 Claims. (C. 91-3) Our invention relates to the production of im degree of acid resistance of enamelware made proved coatings of white enamels and glazes on from frits containing the same, sheet metal, more particularly vitreous enamels Opacifier .- . This material is on a sheet base, - used to a limited extent as a mill addition Opac We have discovered a novel process of enamel ifier. In some enamels percentages of 6% are ing iron, particularly sheet iron, whereby here as effective as 6% Oxlde. tofore unknown and advantageous results in wit The reflectance values for each enamel were reous enamel coatings are attained. One fea determined by means of a reflectometer, and ture of our improved enameling methods con are shown in graphical form in the drawings, sists in the discovery that certain ox O with the percentage mill additions for each opac ides and other opacifiers can be used as mill ad ifer also charted to show the reflectance results dition opacifiers in percentages considerably of each test, he term reflectance is used to higher than heretofore, with unexpected bene conform with modern nomenclature, and in this ficial results in the enamelware produced. case may be taken to indicate the degree of The opacifiers tested in the practice of this opacity or covering power. The visual results invention are as follows: as seen by the eye conform to the reflectance Opacifter A-The zirconium oxide opacifying readings in this series as shown. composition described in the pending applica In the drawings, Figure 1 is a graphical pres tion for patent fled by Charles J. Kinzie Novem entation of the reflectance figures for the enam ber 1, 1938, Serial No. 238,139, which composition 20 els described in Example 1. Figure 2 is a graph consists of over 98% ZrO2 crystals essentially free ical presentation of the reflectance figures for from alkali-metal compounds and is of particle the enamels described in Example 2. Figure 3 size range of 0.40 to 0.90 micron intimately as is a graphical presentation of the reflectance sociated with a dried gelatinous zirconium pre figures for the enamels described in Example 3. clpitate. Figure 4 is a graphical presentation of the re Opacifter B-The zirconium oxide white opac 5. flectance figures for the enamels described in ifying composition described in Example B of Example 4. In the graphs, the letters A, B, C, U. S. Patent No. 2,102,627 of December 21, 1937. D, E, G, H and refer to the opacifiers similar This opacifier contained 88.06% ZrO2. ly identified hereinafter. The letters "S.P.' re Opacifier C.-A high grade tin oxide contain 3) fer to enamels produced in accordance with the ing in excess of 99% SnO and of the grade present invention, while the letters "N. P.' refer usually used in modern tin oxide enamel opaci to enannels produced in accordance with prior fying. art methods. In view of the fact that information available Opacifier D-The zirconium oxide opacifier to the trade is based on enameling tests with described in U. S. Patent No. 1,588,476 of June either tin oxide or zirconium oxide D or zir 15, 1926, to Kinzie, representing the most suc conium oxide B in percentages up to about 5 or cessful commercial zirconium oxide opacifier up 6%, it is not surprising that the effectiveness to quite recent times. of zirconium oxide B in the higher percentages Opacifier E-This consists of a mixture of 75 has not until this time been discovered, and the parts by weight zirconium oxide, Opacifier A, and (0 import of such discovery in developing a new 25 parts by weight of oxide, the latter being enameling technique has not until this time been essentially free from load and and sul disclosed. fates. In modern enameling, the practice is to add Opacifier G-A type of zirconium oxide opaci not in excess of about 3% of the opacifier at fying material with an appreciable silica content the mill along with clay, water, etc. to a so and containing 1 to 2% of water rather firmly called superopaque frit, mill the charge to about fixed by the zirconium or zirconium and silica, 6 to 12 grams residue on a 200 mesh sieve from This HaO is released at enamel firing tempera a 100 cc. slip, and apply the slip in two coats tures, and produces a HaO gas bubble opacity in at a total rate of from 55 to 65 grans per square addition to that produced by the zirconia com SO foot. In one coat practice, the mill addition plex. opacifier is increased to from 4 to 6%, milled to Opacifier H.-- of the grade the same fineness, and is applied at the rate of generally used as a paint pigment. This mate about 45 to 50 grams per square foot in one coat. rial is the most powerful of the paint pigments 55 Reflectance results ranging from 68 to about 72 in pigmenting effects. In enamel manufacture are possible at these rates of application in mod it is often used in the frit batch, due to the fact ern practice. that it is a flux in silicate melts, and has the With the foregoing background, we decided effect of lowering the of the melt that enameling results could be improved by tak and in many cases has a specific effect on the 60 ing advantage of the fact that zirconium , 2 22,011 such as those identified above as Opacifiers A and with mill additions of from 2 to 4 percent tin B, are capable of continuing to increase opacity oxide or zirconium oxide type B. when used as an addition at the mill in amounts Ename formula-Rauty batch (parts by weight) of over 5% and so produce enamelware with the desired reflectance with low enamel application ------49.0 rates. Accordingly, we made millings with 10 to Quartz powder------...-a, -...------5.60 5% and 20% of zirconium oxide B, along with Borax ------28.2 7% clay, A% carbonate and Water, nitrate------5.00 to the fineness as in regular commercial use. Sodium carbonate------4.87 Upon applying the enamel slip to ground-coated O Cryolite ------20 sheet iron and firing the same, however, we Sodium antinonate ------16.00 found that the surface was not passable, the Fluorspar ------5.00 enamel had not smoothed out, doubtless due to inc oxide------2.40 the effect of the ZrO2 adjacent to the carbonate------1.8 frit particles in rendering the same more refrac Titanium oxide------4.00 tory, with the result that these enamels did not Sodium silico fuoride--...------. 4.00 smooth out to the lustrous finish obtained with The raw materials are we mixed and charged an enamel of the same degree of fineness but to the earne frit netting inace at a ten having a lower opacifier addition. perature of about 250 F., ind melted down to After a considerable amount of tests and ex the point where the raw materials combine to perimentation, we found that if the frit in the form a uniform eit which is poured into Water charge carrying the high zirconium oxide B to quench and for the frit, which is the dred. opacifier addition was reduced by milling to a Such frit is of the following calculated compo particle size considerably finer than normally sition: used, or to a point where over 95% by weight of Percent

all the frit particles were at or below 44 microns Na2O--KaO ------. ------a- or a as ran a- - -- 1- 19.19 in size, such an enannel slip could be sprayed onto CaFa ------4.68 metalware in exceedingly thin coatings and fired . Na3AFe ------12 to highly iustrous surfaces having high re ZnO ------2.25 fiectance with a white color and a degree of re 30 Sb2O5 ------12.56 sistance to mechanical abuse far in excess of BO ------9.4 any enamel produced by modern methods. We SiO2 ------3.16 also were surprised to find by calculations that TiO2 ------3.74 the high mill addition opacified enamel in thin AlO ------8.62 coats was more economical, and that in compar ing the raw material costs of our improved meth CaO - ..... ------red a 1- an ar- a- - r rr oa arr p a e - oc op ------O.94 ods on the basis of equal reflectance with present 100.00 practice, our new process gave a lower raw ma Using this frit four separate Enllings were pre terials cost per square foot. pared as follows: We also found that with zirconium oxide B, 4. mill additions of 20 parts by weight of this oxide to 100 parts of frit were most effective in the Milling urbers low rates of application. Fifteen parts by weight were not sufficient, and twenty-five parts by 2 3 weight did not increase opacity enough to war Frt------...... 0 00 rant the added amount. We further found that ------2iron in Oxide A ------10 - O mill additions of 10 parts by weight of zirconium Zircontin oxide B-...... 2 - - - 20 - - -

oxide A gave refectance results at least equival Enameler's clay-----...-- v - v- 7 ent to 20 parts by weight of zirconium oxide B. Water------, - ...... 4. 43 43 43 There appeared no reason for using much more 50 than 10 parts ZrO2. Opacifier A to 100 parts of Mill Enix No. 1 was millied to a fineness of 10 frt in this new process, since this new zirconium grams residue on a 200 Enesh sieve from a 100 cc. oxide is outstanding in its unique opacifying ef sample to represent the normal enameling prac fects when used in our improved methods. tice with this type frit. Mill nix Nos. 12, 13 and We also discovered that the addition of a per 55 4 of this example were milled to a point of cent, or so of zinc oxide which is free of sulfur fineness where nearly all the frit particles were and compounds assisted in the working of under 44 microns in size, or as expressed by sieve our process by making the enamel less refrac fineness test a residue of 1 gran 325 mesh from tory, and also enabled certain enamels to fire a 100 cc. sample. down to smoother, more lustrous coatings. How O Using each of the four slips, enamel specimens ever, the use of zinc oxide at the mill is optional. were prepared by spraying on the enamel at The following examples will fully set forth our rates of application from about 17% grams per invention and discovery whereby enamelware Square foot up to about 62A grams per square foot in steps of 20, 30, 40, 50, 60, etc., all in can be produced with heretofore unknown thin s single coat application over a dark ground coat coatings with high opacity and greatly improved on 6' x 4' panels carefully weighed before and mechanical strength along with increased econ after application. The panels were fired at omy in manufacture. 1520 F. for 2 minutes. Reflectance readings ExAPLE 1. were made for each panel in the series, and from these readings the Figure graphical presenta The frit used is a so-called superopaque frit tion of the results was charted-enamel rate per heavily opacified with compounds, aid square foot against reflectance. is of the type now commonly used to produce As regards reflectance, Figure 1 will be self opaque'results at application rates of 45 to 65 explanatory, and the opacity differences as noted grams per square foot in one and two coats, and s by visual observation are in general in the order 32,0ll 3 of the illustrated reflectance results. In the Using this frit, the following millings were enamels Nos. 12, 13 and 14, good results as to made: texture, surface and lustre were obtained at all rates of application, while in No. 11, the prior Ming numbers normal enameling practice, when the rate was less than 45 grams per square foot, the surface was not good. It will be seen from the graph shown in Fig Frt.------100 100 0000 100

ure 1, that for any point of equal reflectance, Zoiloairconium oxide opacifier - - - - - B-....------6 208 ---...... 8 6 8 much less of the present highly mill addition O 2ircondurn oxide opacifier A.------...-- 20 () opacified enamel is required. Using the mill Zinc oxide------3 5 mixtures as a basis for cost calculations and Water.------...----...----... 40 43 43 43 43 rates of application to equal reflectance, millings Nos. 12, 13 and 14 produce enamel ware at a Milling No. 21 was milled to a fineness of 10 raw materials cost below that of the prior nor 5 grams residue on a 200 mesh sieve from a 100 cc. mal practice of milling No. 11. We also observed sample, while millings Nos. 22, 23, 24 and 25 were that the enameled specimens using millings Nos. each milled to a fineness where more than 95% 12, 13 and 14 carrying enamel at the rate of about by Weight of the frit particles were 44 microns 30 grams per square foot would stand nearly or smaller, or a residue of about one gram --325 twice as much flexing of the sheet metal as com 20 Enesh from 100 cc. of slip, pared with the prior normal process enamel No. Using each slip, panels were prepared by spray 11 applied at the 50 grams per square foot rate. ing the enamel over a dark ground coat using We also observed that when the steel was dis 6' x 4' panels at single cover coat application torted by a under pressure that the 30 rates varying from about 20 to 60 grams per grams per square foot applications of enamels 2. square foot. The panels were fired at 1520 F, Nos. 12, 13 and 14 showed only slight fracturing, for 2% minutes, cooled, and then the reflectance while the 50 grams per square foot application was determined on each. The reflectance results of No. 11 was badly fractured, the enamel de of the series are set forth in Figure 2 which taching over a large area. Therefore, in addi shows the reflectance at the different rates of tion to the procurement of desired opacity or 30 application for each of the five enamels. The reflectance at a low rate of application, the re observations as to apparent covering power sultant enamel finish is superior in mechanical strength and adherence and hence will stand con or Opacity when the panels were examined siderably more abuse. This matter of thin films visually appear generally of the same order with improved strength has been a long-felt want 35 as expressed by the percent reflectance of on the part of enamelers and users of enamel Figure 2. All flve enamels had good surfaces. ware, but heretofore it has been impossible of Nos. 24 and 25, in particular, had brilliant sur attainment, since no process was known by which faces and were very resistant to scratching and sufficient opacity could be obtained along with Wear. high lustre and other desired properties. 40 Viewed from the standpoint of economy, the process of enameling as presented by millings ExAMPLE 2 Nos. 22, 23, 24 and 25 of this Example 2, repre The frit prepared and used in this example sents considerably greater advantages when was an antimony free zirconium composition of Compared with Example , due to the fact that the following formula: the frit is considerably lower in cost. The en Batch formula-Parts by Deight amels are superior from the standpoint of hav ing greater lustre, smoother and more brilliant Pyrophyllite ------38.06 surfaces, and have considerably greater resist Borax crystals------36.10 50 ance to scratching and abrasion than any enamel Fluorspar------amon - 'a - as a mar - - 5.65 Zirconium silicate 325 mesh.------16.53 of the Example 1 series. Zinc oxide------7.18 This frit of Example 2 is not particularly Cryolite ------7.35 opaque in the frit stage, but certain ingredients Quartz powder------6.03 in the frit appear to cooperate with the mill Sodium nitrate------40 SS added zirconia in developing a degree of opacity hardly to be expected from a frit of its appear Sodium carbonate------4.15 ance. It is believed that the mill added zirconia 123,15 acts as an exciter or catalyst, thereby causing The batch was well mixed and then smelted 60 the crystallization of opacifying particles to sepa in a frit furnace and poured into water to rate in the frt during the firing on of the en quench, and the resulting frit was then dried. amel, and this opacity along with that of the The calculated melted composition of this enamel mill added zirconda explains the high degree of , frit was as follows: opacity finally existing in the fired enamel. Percent 35 Na2O--Kao------13.0 ExAMPLE 3 Cala------5.65 ZnO------.18 Example 3 represents the adaptation of our Alaos------10.44 new enameling process to an enamel of the acid ZrO2------an a-am as a is 10.5 O resisting type. SiOa------37.40 The following batch of raw materials was well BaOS ------3.21. mixed and then smelted to a honogeneous melt F------2.30 which was poured into water and the resulting 100.00 5 frit was dried. 4 22,011 Batch formula-Parts by weight present and the antimony content was a percent Sodium nitrate------8.4 or two lower. This frit, although of the super Antimony oxide------it - - -- a-- r man m - a - - - - - 16.2 opaque type, does not yield quite as high opacity Phosphate rock.------5.8 in this process as do the frits of Examples 1 and Titanium oxide------19.0 2, but is high enough to be entirely practical in Quartz powder------59.4 Our process. Sodium carbonate------25.0 With this superopaque frit we made millings Pork ------51.2 using: Sodium silico fluoride------15.0 O Frit ------100 The frit was of the following calculated com Enameler's clay------7 position: Opacifier------20-or otherwise Percent as indicated Na2O------20.2 in Figura 4. CO------18 5 Water ------43 S.O. ------10.5 SO? ------4.1.8 Each charge was milled to a fineness of prac PO ------2. tically all minus 44 microns. A series of 6' x 4'' TO ------12.3 sheet iron panels was prepared in one coat at FOs ------1.3 various application rates. Readings were made for each, and these reflectance readings are pre 100.0 Sented in graphical form in Figure 4. Various ones of the previously listed opacifiers were Using this acid-resisting frit, the following tested, with the following comments as to color, millings were made: lustre and other results: Opacifier B (2irconium oacide)-20% of this Milling numbers material gave good results as to reflectance, lustre and color and worked well throughout the 31 32 33 34 enamel process. 3) Opacifier C (tin oacide).-The reflectance in

Frit------...... 100 100 100 10 Enameler's clay ...... 2 2 2 2 parted by tin oxide was higher than zirconium Setting up powder for slip" ---- 3 3 3. 3 Zirconium oxide opacifier B-----. . . . . 6 2 oxide D, but not as high as zirconium oxide B. Zirconium oxide opacifier A.------...... 10 In The lustre was lower in the case of the tin oxide Zinc oxide ------3 enlannel Specimen. As to color it was found that Water...... - 40 43 43 43 the tin oxide enamel was too much of an ivory The powder referred to is a setting up and suspending agent and in color and could not be classed as a white in is described in Example C of U.S. Patient No. 1.85 of January Comparison with enamels in which either zir 22, 1935. conium oxide B or D were used. In mix No. 31, the milling was as for normal Opacifier D (2irconium oacide) - This gave practice, namely, to a fineness of about 10 grams O an enamel with very good lustre and white color residue on 200 mesh sieve from a 100 cc. sample and worked well in the process, but does not of slip. In mixes Nos. 32, 33 and 34, the mixes yield as high reflectance as did zirconium oxide were milled to a point where nearly all the frit Opacifier B. particles were 44 microns or finer, and expressed Opacifier E (airconium oacide plus 2inic Oc in sieve test terms a residue of 'A of 1 percent ide).-20% mill addition results show this opaci fler to be the most powerful of this series as re slip.remained on a 325 mesh sieve from the 100 cc. gards reflectance excepting cerium oxide e Using each of these slips and 6' x 4' ' dark amel below the 30 gram rate. The color was ground coated panels, the enamel was applied good and the lustre fairly good. Since there is a various rates in one coat only and the speci f no point in using such a high percentage of mens fired at 1520 F. for 2% minutes. Refer this product, a milling was made with 13.2% and tance readings were taken for each enameled the reflectance results are included as to re Specimen, and the percent reflectance for each flectance in the rates up to about 30 grams per of the four enamels at various application rates square foot, 13.2%. Opacifier E gave a higher are shown graphically on the accompanying reading than any other opacifier in this series Figure 3. The observations as to apparent excepting titanium oxide or cerium oxide. Above Opacity are generally of the same order as of 30 grams per square foot rates, 13.2%. Opacifier the reflectance percentages found. E excelled the 20% addition of all others. The We do not confine this invention to the par 13.2% of Opacifier E gave an enamel of excelling ticular types of zirconium oxide opacifiers re lustre, white color, fine surface and texture, and ferred to, nor do we confine it only to zirconium the enannel behaved in excellent manner through oxides, but wish to embrace the use of other pos out the process. The opacity is a function of sible materials having the properties of and used the zirconium oxide present plus the enamel frit as mill addition opacifiers. We have made tests opacity, while the zinc oxide assists in producing with high percentages of a number of such mill t a highly lustrous surface. addition opacifiers in our new process, as shown Opacifier G (2ircontin Oacide).-In normal en in the following example. amel practice where up to 6% of this product is used at the mill, the resulting enamel lustre ExAMPLE 4 is lowered. As will be seen, a 20% mill addi In this series of tests We used a frit of the tion of this opacifier produced reflectance re superopaque type of erranel frits for use Cn sheet sults above those for zirconium oxide type D iron. An analysis of this frit shows it to b?e and below those for zirconium oxide type B. The heavily opacifled with antimony compounds and lustre of enamels containing 20% Opacifier G more or less of the same composition as the frit was very poor in all cases, and there developed used in Example 1, except that no titanium was 75 serious defects in enameling, particularly a tear 22,011 S ing of the film during the operation. The Opacil foot of surface when fired. These dark ground fier G opacity was fairly good. coats have practically no reflectance and re Opacifer (titanium oxide).-Normally this flectance readings may vary from nearly 0 to oxide of titanium is not used at the mill except about 7. The reason we have referred to such in low percentages of 1 to 2% to improve the s dark colored ground coats as being used in our lustre, and not as an opacifier, since it goes into process is that these coats are in commercial use solution readily during the firing on of the en at the present time. amel film. We tried this TiO, as a 20% addi However, we do not limit our invention to the tion in our new process. The figure 4 re application of our enamel Over a conventional flectance results show that, in the application dark colored ground coat. For example, our new rate up to 30 grams per square foot, the TiO2 process of Superopaque vitreous enameling could was very effective in increasing the reflectance, be used in conjunction with the enamel for direct and that at higher rates this TiO2 in this en application on metal disclosed in U. S. Patent No. amel did not vary in reflectance, being unusual 1,944,938 to Kinzie, By using the slip prepared in this respect. The enamels were entirely matte s according to the Example A formula and pro non-lustrous surfaces above 30 grams per square cedure of this U. S. Patent No. 1944,938 and ap foot, with only a fair lustre at lower rates. The plying the slip directly to the prepared iron base color was of a yellow order and not white. While at the rate of about 25 grams per square foot zirconium oxide as a mill addition in enamel surface, firing this and applying our new process produces a white opacity in all types of enan 2 enamel such as milling No. 24 at the rate of 20 els, titanium oxide seldom does. The color ef grams per square foot, we produce white vitreous fect will vary depending on the composition of enamel in the Superopaque white class with an the enamel frit, the mill additions, and the extremely low rate of application. treatment received in the processing, etc. In the There is also in use, particularly in the vitreous case of the 20% mill addition of TiO2 in this enameling of sheet iron culinary Ware, a process example, a considerable amount of the TiO2 must in which the iron shape is first coated with a light have dissolved to form a glass of high index of colored ground coat having some opercity and a refraction with the separation of crystalline reflectance of about 25. Over this ground coat compounds to form the matte surface obtained. is applied a more opaque enamel in one coat, but Opacifier I (cerdan olde) - The reflectance S the finish coat enamels up to this time have not results with 20% of cerium oxide Opacifier are been opeque enough. For first class Ware it has shown in Figure 4. In reflectance results the been necessary to apply two cover coats over the behavior of this material was similar to titanium light colored ground coat. We will now illus oxide, but cerium oxide produced enamels of trate a case in which we apply Our new process fairly good lustre at all rates, although there 3. to such a ground coat. was some film tearing on the panels. Cerium oxide is rather soluble in glasses, enamels, etc. ExAPLE 5 and like the TiOa this cerium oxide must have The ground coat frit is prepared by mixing and dissolved to a considerable extent, thereby in then melting the following batch, pouring the creasing the index of refraction of the glass and AU) melt into water to produce the frit: apparently making the enamel more refractory. In color the enamels containing this cerium Batch formula-Parts by tipeight oxide were bluish or gray white in color tone, and Feldspar ------32.0 the enamels were easily scratched. Borax ------SS For purposes of comparison, Figure 4 carries Quartz powder---...------8.0 a curve showing the effect of this particular en Fluorspar ------4.3 amel when milled to the prior normal fineness Calcium carbonate------2.2 with a mill addition of 2% tin oxide. Sodium nitrate------2.4 These experiments with various mill addition Soda ash------8. opacifiers serve to prove that the most eficient s oxide------0. material is the zirconium oxide A type opacifier, and that zirconium oxides B and D are next in The calculated composition of the frit was: importance in respect to enamel lustre, white Percent ness of color, and opacity. Nevertheless they NazOK2O ------9.6 show that certain other types of material do s Caia ------5. function to a certain extent. Hence we include CaO ------15 such substances within the scope of our improved Al2O3 ------as s m so is a a neue masq m raus as mosun as as 7.79 process, since in certain classes of ware, the SiOa ------490 whiteness of color and high lustre may be sec BaO ------8.00 ondary, and possibly the defects observed in cer 6 CoO ------0.3 tain of these materials, such as tearing of the film might be overcome. Hence we include in 100.00 this process of enameling opacifying mill add tions such as tin oxide, titanium oxide and 100 parts of this frit were milled with 7 parts cerium oxide. of enameler's clay, 6 parts of drconium oddle The oxides of and are known Opacifier D, 0.25 part of magnesium carbonate, to be stable white refractory oxides having a and 0.10% part of sodium nitrite, a milled to a relatively high index of refraction and generally fineness of 8 grams residue On a 200 mesh seve close to zirconium in properties. These oxides from 100 cc. sample. This slip was applied so as are of interest in our improved process, but their to produce 23 grams of ename per square foot cost is prohibitive at the present time, surface when fired at 1540' E. for 2 minutes, Most of the commercial white vitreous en This light colored ground coat had what might ameling on sheet iron involves the use of a dark be described as an opalescent appearance, and colored ground coat usually applied by dipping had a reflectance reading of 16. A coating of and draining at the rate of 18 grams per square 75 milling No. 24 was applied and fired at 1520 F. 6 22,011 for 22 minutes yielding a fired coat of 21.6 grams iron in two coats at a total of 72 grams per square per square foot. This enamel was of a degree of foot, will have a reflectance of about 60. Pref whiteness and apparent opacity equal to the so erably a reflectance reading of 70 or above is called white enamel cooking ware having twice desired. (See Reflectance Test for Opaque White the weight of enamel on the iron. The reflect Vitreous Enamels-published March, 1937, by ance reading was 58.3. n Tech. Research Section Educational Bureau Por In another test in the same light colored ground celain Enamel Institute-612 N. Michigan Ave., coat, a coating of milling No. 24 was applied and Chicago, Ill.) fired at 1520' F. 22 minutes to yield 29.4 grams We do not wish to limit the process to the of enamel per square foot over the ground coat. U particular proportions of frit, opacifier and other This enamel had a reflectance reading of 64.8, mill additions. We have, for instance, made mill and was of an order of whiteness and opacity ings to about 20 microns of frit particles with as desired in high quality ware. The lustre was high as 40 percent ZrO2 opacifier at the mill with high and the surface excellent for each rate of interesting laboratory enameling results and high application. degree of opacity at rates as low as 8 grams per Economy, improved quality as to mechanical square foot. This is a possible development com strength, along with excellence as to finish, are mercially for this process when the technique of possible by this method. application is understood to a degree greater than In enamel practice, it is common to add cer at present. Commercially there appear to be h tain electrolytes to increase the set of enamel or in certain lower limits to the rate of application, ill some cases to decrease it. So in our improved mainly due to the dark ground coating practice process We may, if necessary, resort to such use used as well as to the equipment available for of small amounts of electrolytes, but usually the handling the process. At the moment our efforts characteristics of the slips, particularly those commercially are to replace the present normal Opacified with zirconium oxides A, B and D, are : process of one cover coat application at the rate Stich that little or no additions are required. of 45 to 50 grams per square foot by our new Where required it appears that from A to A of process in one coat at the rate of 25 to 35 grams one part by weight of sodium nitrite to each 100 per square foot, and to replace present normal parts of frit used is an advantageous addition. two cover coat practice of about 60 to 80 grams For reflectance study purposes, the various : per square foot, either by one coat by our new enamels were applied by spraying with the use of process at the rate of about 30 to 40 grams per a spray gun and nozzles of the type and size com square foot or in Some cases apply our heavily monly used in the spraying of organic coatings mill opacified finely milled enamel in two coats, such as paints and lacquers. The prior normal the first coat at about 20 to 25 grams per square millings (Nos. 11, 21 and 31) were applied by use 35 foot and a finish coat of from 15 to 10 grams per of the usual type of Spray gun used for vitreous square foot. Our improved processes therefore enannel slips. are not strictly limited to a single cover coat We do not confine such enamel applications, application, but have been practiced with out however, to the spraying method. Excellent standingly good results in two very thin coats; enameling results have been obtained by the tong 40 this latter method must be resorted to in some dipping method commonly used in the vitreous types of work where extra high quality is re enameling or iron culinary ware. Excellent re quired as to freedom from enamel defects, Sults have been obtained by dipping, for instance We have also found zirconium oxide of the in acid-resisting enamels of the type illustrated types referred to as Opacifiers A, B and D yield in millings Nos. 32, 33 and 34, and particularly superior results by this new process when com Nos. 33 and 34. Where the acid resistance is not pared with other available mill addition opacifiers required to be complete, the dipping process gives as to resultant Opacity, lustre, whiteness and gen good results with millings Nos. 22 to 25, and par eral process workability, We prefer the types. A ticularly No. 24, for culinary ware and other and B, but zirconium oxide opacifier type D should types of enamel practice where the slip is cus not be overlooked, in view of the fact that it tomarily applied by the dipping process. Fine yields enamel of very high lustre, white color opaque white lustrous enamel results have there and excellent workability. More of it must be used than is the case of either A or B type by been produced in One thin coat over the dark opacifiers. ground coat, the single cover coating being ap Reasonably satisfactory mill addition opacifiers plied at rates of 20 to 30 grams per square foot, are those which can be used in the high percent while in comparison the normal practice is to ages to produce lustrous opaque white enamel deposit enamel at from 45 to 80 grams per square finishes at rates of about 10 grams per square foot to obtain sufficient coverage in enamelware foot up to about 40 grams per square foot. Such for culinary usage. mill addition opacifiers can be described as ex We do not limit ourselves to the particular tremely fine powders having a enamel frits set forth in these examples, as ob above 1.8, preferably above 2.00, which are stable viously many other enamel formulae may be used or essentially so in contact with the fused enamel in making frits satisfactory for this process, and frit particles during the firing of the enamel in fact we have tried the process in at least twelve onto the ware, and also capable of being used different enamel frits with successful results as in such amounts at the mill so as to produce to coverage when our new high opacity fine mill opaque coatings having a reflect ing process is used. Among the enamel frits ance of more than 70 when applied at a rate of which are satisfactory for our new and improved 40 or less grams per square foot. process are opaque white frits which when milled We prefer, however, to use a heat stable white 100 parts by weight of frit, 6 parts by weight val dioxide of any element of the fourth group of lendar clay, 0.25 part by weight of magnesium Mendeleefs Periodic System which forms no oxide carbonate, 40 parts by weight of water to a fine Iower than the dioxide. Only zirconium, hafnium ness of 12 grams residue on a 200 mesh sieve from and thorium fulfill these requirements, since the a 100 cc, sample applied to ground COated sheet dioxides of titanium, tin, etc. are reduced to

22,011 7 lower dark-colored oxides when subjected to re by weight of the particles thereof are less than ducing conditions. While such reducing cond 44 microns in size to form the enamel slip, ap tions are not generally met with in vitreous plying the said slip to ground coated ware in a enameling practice, they can occur, and our thin film not exceeding 40 grams per square foot alm is to establish conditions in the procedure when fired, and burning the slip-coated ware at which will be least likely to cause discoloration. firing temperatures to produce said adherent vitreous enamel Ware. Since hafnium is relatively rare and prohibitive 4. The method of making white vitreous as to price, and since thorium is also extremely enamel ware with coatings less in weight than high in price, the dioxide of zirconium remains 40 grams per square foot and having a reflectance as the preferred dioxide and particularly in the above 70 and substantially greater than that forms as referred to as opacifiers A, B and D producible with the frit used and clay alone, which we have found to be suitable for this which comprises milling a mixture of a white process. frit 100 parts by weight having a basic reflectance Paint pigment oxides such as zinc oxide and above 60, clay, water and from about 10 to 20 lead oxides, although having a relatively high parts by weight of Zirconium dioxide, said mix index of refraction, are ineffective primary opacil ture being ground to a fineness where more than flers in our process, since these oxides are power 95% by weight of the particles thereof are less ful fluxes, combining avidly with the enamel to than 44 nicrons in size to form the ename slip, form more fluid glasses. For this reason a certain applying the said slip to ground coated Ware in amount of such material added at the mill is in a thin film not exceeding 40 grams per square certain cases desirable not from the opacity foot when fired, and burning the slip-coated Ware standpoint, but because such addition renders the at fring temperatures to produce said adherent coating less refractory and more readily fused vitreous ename Ware. down to a lustrous smooth finish. 5. The method of making white vitreous Where parts and percentages are mentioned, enamel ware with coatings less in weight than parts by weight are understood. 40 grams per square foot and having a reflectance We can: above 70 and substantially greater than that pro 1. The method of making white vitreous ducible with the frit used and clay alone, which enamel ware with coatings less in Weight than comprises milling a mixture of a white frit 100 40 grams per square foot and having a re parts by weight having a basic reflectance above flectance above 70 and substantially greater than 60, clay, water and not less than 10 parts by that producible with the frit used and clay alone, weight of zirconium dioxide and from 3 to 5 which comprises milling a mixture of a white parts of zinc oxide essentially free from lead and frit 100 parts by weight having a basic re sulfur compounds, said mixture being ground flectance above 60, clay, water and not less than to a fineness where more than 95% by weight of 10 parts by weight of an opacifier selected from the particles thereof are less than 44 microns the dioxides of the group consisting of zirconium, in size to form the enamel slip, applying the said tin, titanium, hafnium, thorium and cerium, said slip to ground coated ware in a thin film not mixture being ground to a fineness where more exceeding 40 grams per square foot when fired, than 95% by weight of the particles thereof are and burning the slip-coated ware at firing tem less than 44 microns in size to form the enamel peratures to produce said adherent vitreous slip, applying the said slip to ground coated eane Ware. Ware in a thin film not exceeding 40 grams per 8, The method of making white vitreous enam Square foot when fired, and burning the slip el ware with coatings less in weight than 40 coated ware at firing temperatures to produce s grams per square foot and having a reflectance said adherent vitreous enamel ware. above 70 and substantially greater than that 2. The method of making white vitreous producible with the frit used and clay alone, enamel ware with coatings less in weight than which comprises milling a mixture of a white 40 grams per square foot and having a reflectance frit 100 parts by weight having a basic reflectance above 70 and substantially greater than that pro St. above 60, clay, water and from about 10 to 20 ducible with the frit used and clay alone, which parts by weight of zirconium dioxide and from comprises milling a mixture of a white frit 100 3 to 5 parts of zinc oxide essentially free from parts by weight having a basic reflectance above lead and sulfur compounds, said mixture being 60, clay, water and from about 10 to 20 parts ground to a fineness where more than 95% by by weight of an opacifer selected from the di 55 weight of the particles thereof are less than 44 Oxides of the group consisting of zirconium, tin, microns in size to form the enamel slip, apply titanium, hafnium, thorium and cerium, said ing the said slip to ground coated ware in a mixture being ground to a flneness where more thin film not exceeding 40 grams per square foot than 95% by weight of the particles thereof are when fired, and burning the slip-coated ware at less than 44 microns in size to form the enamel ts) firing temperatures to produce said adherent slip, applying the said slip to ground coated ware vitreous enamel ware. in a thin film not exceeding 40 grains per square 7. The method of making white vitreous enam foot when fired, and burning the slip-coated el ware with coatings less in weight than 40 ware at firing temperatures to produce said ad grams per square foot and having a reflectance herent vitreous enannel Ware. 3. The method of making white vitreous above 70 and substantially greater than that pro enamel ware with coatings less in Weight than ducible with the frit used and clay alone, which 40 grams per square foot and having a reflectance comprises milling a mixture of a white frit 100 above 70 and substantially greater than that parts by weight having a high aluminum and producible with the frit used and clay alone, zirconium content, clay, water and not less than which comprises milling a mixture of a white 10 parts by weight of an opacifier selected from frit 100 parts by weight having a basic reflectance the dioxides of the group consisting of zirconium, above 60, clay, Water and not less than 10 parts tin, titanium, hafnium, thorium and cerium, said by weight of zirconium dioxide, said mixture be mixture being ground to a fineness where more ing ground to a fineness where more than 95% S than 95% by weight of the particles thereof are S 22,011 less than 44 microns in size to form the enamel enamel ware having a coating in weight of about slip, applying the said slip to ground coated ware 30 grams per square foot and a reflectance above in a thin film not exceeding 40 grams per Square 70 and substantially greater than that producible foot when fired, and burning the slip-coated Ware with the frit used and clay alone, the steps which at firing temperatures to produce said adherent consist in milling with water a mixture of a Vitreous enlannel Ware. white frit 100 parts by Weight and about 13 parts 8. The method of making white Witreous enan of an opacifier comprising zirconium dioxide and el ware with coatings less in Weight than 40 Zinc oxide in the ratio of 3 to 1, said mixture grams per square foot and having a reflectance being ground to particle fineness of less than above 70 and substantially greater than that O 44 microns to form the enamel slip, and apply roducible with the frit used and clay alone, ing said slip to said ware which upon drying and which comprises milling a mixture of a white firing will produce aforesaid white vitreous coat frit 100 parts by weight having a high aluminum ing characterized also as having a highly lustrous and zirconium content, clay, water and not less surface and fine texture. than 10 parts by weight of Zirconium dioxide, 13. In the method of making white vitreous said mixture being ground to a fineness where enamel Ware having a coating less in Weight more than 95% by weight of the particles there than 40 grams per square foot and a reflectance of are less than 44 microns in size to form the above 70 and substantially greater than that pro enamel slip, applying the said slip to ground ducible with the frit used and clay alone, the coated ware in a thin film not exceeding 40 20 steps which consist in milling a white frit mixed grams per square foot when fired, and burning with from 10 to 20 parts by weight of an opacil the slip-coated ware at firing temperatures to fler selected from the dioxides of the group con produce said adherent vitreous enamel ware. sisting of zirconium, tin, titanium, hafnium, 9. The method of making white vitreous enan thorium and cerium to 100 parts of said frit in el ware with coatings less in weight than 40 25 Water, said mixture being ground to a particle grams per square foot and having a reflectance fineness of less than 44 microns to form the above 70 and substantially greater than that pro enamel slip, and applying said slip to said ware ducible with the frit used and clay alone, Which in a thin flin which upon drying and firing will comprises milling a mixture of a white frit 100 produce the aforesaid white vitreous coating hav parts by weight having a high aluminum and 30 ing an opacifier content of more than 18 per zirconium content, clay, Water and not less than cent. 10 parts by weight of zirconium dioxide and from 14. The method of making white vitreous 3 to 5 parts of zinc oxide essentially free from enamel Ware with coatings less in weight than lead and sulfur compounds, said mixture being 40 grams per square foot and having a refect ground to a fineness where more than 95% by 35 ance above 70 and substantially greater than that weight of the particles thereof are less than 44 producible with the frit used and clay alone, microns in size to form the enamel slip, apply which comprises milling a mixture containing ing the said slip to ground coated Ware in a 100 parts by Weight of a white frit, clay, water thin film not exceeding 40 grams per square and not less than 10 parts by weight of an opaci foot when fired, and burning the slip-coated ware O fier selected from the dioxides of the group con at firing temperatures to produce said adherent sisting of Zirconium, tin, titanium, hafnium, vitreous enamel Ware. w thorium and cerium, said mixture being ground 10. In the method of making White vitreous to a fineness where more than 95% by weight enamel ware having a coating less in weight of the particles thereof are less than 44 microns than 40 grams per square foot and a reflectance 5 in size to form the enamel slip, applying the above 70 and substantially greater than that pro said slip to ground coated ware in a thin film ducible with the frit used and clay alone, the not exceeding 40 grams per square foot when steps which consist in milling a white high alumi fired, and burning the slip-coated ware at firing num and zirconium containing frit mixed with temperatures to produce said adherent vitreous from 10 to 20 parts by weight of 2irconium diox enamel ware. ide to 100 parts of said frit in water, said mix 15. The method of making white vitreous ture being ground to particle fineness of less enamel ware with coatings less in weight than 40 than 44 microns to form the enamel slip, and grams per Square foot and having a reflectance applying said slip to said ware which upon dry above 70 and substantlally greater than that pro ing and firing will produce aforesaid White wit 5 ducible with the frit used and clay alone, which reous coating having a zirconium dioxide con comprises milling a mixture containing 100 parts tent of more than 16 percent. by weight of a white frit, clay, water and from 11. In the method of making white vitreous about 10 to 20 parts by weight of an opacifier enamel ware having a coating less in weight selected from the dioxides of the group consist than 40 grams per square foot and a reflectance O ing of zirconium, tin, titanium, hafnium, thori above 70 and substantially greater than that pro urn and cerium, said mixture being ground to a ducible with the frit used and clay alone, the fineness where more than 95% by weight of the steps which consist in milling a white high alu particles thereof are less than 44 micrors in minum and zirconium containing frit mixed with size to form the enamel slip, applying the said from 10 to 20 parts by weight of zirconium diox slip to ground coated ware in a thin film not ex ide and from 3 to 5 parts of zinc oxide essen ceeding 40 grams per square foot when fired, and tially free from lead and sulfur compounds to burning the slip-coated ware at firing tempera 100 parts of said frit in water, said mixture being tures to produce said adherent vitreous enamel ground to particle fineness of less than 44 mi We. crons to form the enamel slip, and applying said 16. The method of making white vitreous slip to said ware which upon drying and firing enamel ware with Coatings less in weight than 40 will produce aforesaid white vitreous coating grams per Square foot and having a reflectance having a zirconium dioxide content of more than above 70 and substantially greater than that pro 16 percent. ducible with the frit used and clay alone, which 12. In the method of making white vitreous comprises milling a mixture containing 100 parts 22,011 9 by weight of a white frit, clay, water and not by weight of a white frit, clay, water and not less less than 10 parts by weight of Zirconium dioxide than 10 parts by weight of zirconium dioxide, and from 3 to 5 parts of zinc oxide essentially said mixture being ground to a fineness where free from lead and sulfur compounds, said mix more than 95% by weight of the particles thereof ture being ground to a fineness where more than are less than 44 microns in size to form the 95% by weight of the particles thereof are less enamel slip, applying the said slip to ground than 44 microns in size to form the enamel slip, coated ware in a thin film not exceeding 40 grams applying the said slip to ground coated ware in per square foot when fired, and burning the slip a thin film not exceeding 40 grams per square coated ware at firing temperatures to produce foot when fired, and burning the slip-coated ware said adherent vitreous ename ware. 10 at firing temperatures to produce said adherent 17. The method of making, white vitreous vitreous enannel Ware. enamel ware with coatings less in weight than 40 19. The method of making white vitreous grams per square foot and having a reflectance enamel ware with coatings less in weight than above 70 and substantially greater than that pro 40 grams per square foot and having a reflectance ducible With the frit used and clay alone, which 5 above 70 and substantially greater than that pro comprises milling a mixture containing 100 parts ducible with the frit used and clay alone, which by weight of a white frit, clay, water and from comprises milling a mixture containing 100 parts about 10 to 20 parts by weight of zirconium di by Weight of a White frit, clay, water and from oxide, said mixture being ground to a fineness about 10 to 20 parts by weight of zirconium d where more than 95% by weight of the particles oxide and from 3 to 5 parts of zinc oxide essen thereof are less than 44 microns in size to form tially free from lead and sulfur compounds, said the enamel slip, applying the said slip to ground mixture being ground to a fineness where more coated ware in a thin film not exceeding 40 than 95% by weight of the particles thereof are grams per square foot when fired, and burning less than 44 microns in size to form the enamel the slip-coated ware at firing temperatures to 25 slip, applying the said slip to ground coated ware produce said adherent vitreous enamel Ware. 18. The method of making White vitreous in a thin film not exceeding 40 grams per square enamel ware with coatings less in Weight than 40 foot when fired, and burning the slip-coated ware grams per square foot and having a reflectance at flring temperatures to produce Said adherent above 70 and substantially greater than that pro 30 vitreous enamel ware. ducible with the frit used and clay alone, which CHARLES J. KNZE. comprises milling a mixture containing 100 parts CHARLES H. COMMONS, JR. CERTIFICATE OF CORRECTION. Reissue No. 22, Oll. January 20, l942. CHARLES J. KINZIE, ET AL. It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page l, first column, line 42, for "load" read -- lead--; page l, first column, line 50, for "a various" read -- at various -- ; and that the said Letters Patent should be read with this correction there in that the same may conform to the record of the case in the Patent Office. Signed and sealed this 17th day of March, A. D. l942.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.