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Home , Potassium oxide

Patented Apr. 7, 1942 2,278,867 UNITED STATES PATENT OFFICE 2,278,867 -FREE GLAZE OF LOW MATURNG TEMPERATURE FOR USE IN DECORATING CERAMCWARE Alden J. Deyrup, Elizabeth, N.J., assignor to E. ... " du Pont de Nemours & Company, Wilmington, Del, a corporation of Delaware No Drawing. Application May 1, 1940, Seria No. 332,732 9 Claims. (C. 106-48) This invention relates to certain improved lead temperature of glaze firing, being utilized. The free glazes or fluxes of the type suitable for use temperature employed in the overglazing fire to in art-glazing or Overglazing ceramic ware. More mature the overglaze is usually 700 to 800' C., particularly, this invention relates to certain new which is of course considérably.lower than the and improved flux compositions free from leadi 5 temperature range in which the glazes used to which, when used for the artglazing or coat the bisque are fired. At this overglaze fir Overglazing of chinaware and pottery, are capa ing temperature the colored decorative coating ble of melting at fairly low maturing tempera matures and vitrifles, and the ware is thus coat tures to a superior decorative coating of high ed with a colored decorative surface having a resistance to both the action of chemical agents 10 high degree of glossiness. such as acids and alkalies, and to mechanical Bisque ware is sometimes decorated by plac abrasion. ing on the surface of the ware, without prelimi In the manufacture of china and pottery a narily coating the surface of the bisque with a clay mixture is customarily formed into the de vitrified glaze, a mixture of pigment and low sired shape and then fired at a high tempera 15 melting flux which can be matured to a good ture, one within the range 1250 to 1400° C. being gloss in the overglazing fire and at the tempera ordinarily employed. The product resulting from ture of Overglazing. The colored flux composi this first firing is known as bisque. The bisque, tion may be applied by dipping the bisque in the while hard, is more or less porous in structure. mixture of pigment and low-melting flux, or any Moreover, the surface is generally rough and de 20 other method such as spraying the bisque ware void of glossiness. with the composition may be employed to coat In manufacturing chinaware and pottery from the bisque surface, in accordance with proce bisque, bisque is usually coated with a glaze com dures which are now well understood in the position. This can readily be done by dipping manufacture of chinaware and pottery. This or spraying the bisque with an aqueous suspen type of decoration is often called 'artglazing,” sion of the flux or glaze composition, and then and the term artglaze ordinarily signifies a vitri Subjecting the coated product to a second firing. fiable color composition which can be applied di * The second firing, usually carried out at a fairly rectly to bisque ware (without intermediate glaz high temperature but one below the tempera ing) and matured in a decorating kiln to a ture of bisque firing, temperatures of 1100 to 30 colored glossy decorative coating at the same tem 1300 C. being common, causes the glaze to melt peratures used to mature overglaze decorative or mature on the ware and form a smooth, vitre coatings, 700 to 800° C. Ous surface coating. The ceramic ware is often The use of a glaze stain in a glaze for forming colored by means of a pigment dispersed in this a decorative coating on bisque ware will result glaze slip or suspension which is fired on the in an article similar to ware coated by the use bisque. A pigment utilized for this purpose is of an artglaze on bisquie. Both methods of dec ordinarily referred to as a glaze stain, and a rea orating are capable of producing ceramic ware sonably uniform color over the entire body can formed with a uniformly colored vitreous layer readily be secured by suspending a suitable pig over the entire surface of the article. The prin ment in the glaze composition. 40 cipal advantage accruing to the use of an art It is also possible to decorate the ceramic ware glaze, as compared with the decoration of bisque with a colored decorative surface coating by over Ware by means of a glaze pigmented with a glaze glaze color application. A mixture of the pig stain, results from the fact that lowerfusion tem ment in a flux of a relatively low maturing tem peratures may be employed in artglazing and this perature, known in the art as an overglaze color, permits the use of some pigments, chiefly the may be applied over the glaze formed on the red pigments, which are unstable at bisque by the first or glaze firing. This over the higher firing temperatures required to ma glaze composition, suspended in a suitable ve ture a regular glaze on the bisque. Decorating hicle, may of course be applied to the bisque body the ware by means of an artglaze gives the man coated with the glaze composition by spraying, 50 ufacturer a wider palette and permits the use brushing, or by any other convenient method of more brilliant colors. Another advantage in employed in the art for coating ceramic ware herent in the use of artglazes as contrasted with with glaze compositions. The ware is then fired ... regular glazes is that breakage occurs much less at a relatively low temperature, one lower than frequently at the temperatures employed in over either the temperature of bisque firing, or the 55 glazing than at the higher temperatures employed

- sv 2 2,278,867 in the glaze fire. This reduction in the occur will be apparent from the ensuing disclosure of rence of breakage rests in substantial reduction certain improved embodiments thereof. in the number of unsatisfactory products, known My improved glaze compositions, suitable for in the industry as "rejects.' use as artglaze fluxes, are characterized by the While the artglazes possess certain advantages absence of lead oxide and by the fact that while Over regular glazes, they have also had some dis compounds of lead are not present therein the advantages as compared with the higher-melt glazes nevertheless mature to glossy decorative ing glaze compositions which are applied to coatings at the low temperatures used in Over bisque when that product is coated with the regul glazing. While fluxes and glazes which contain lar glaze. The chief disadvantage of overglazes 10 no lead oxide are already known to the art, such has been, in the past, their lack of resistance to compositions in the past have either had very the action of acids, as well as the necessity for high melting points or coefficients of expansion including lead oxide in the composition in order too high to permit application of the glaze, even to secure a suitable maturing temperature. It in a very thin layer, on top of chinaware which has been considered essential to have lead oxide 5 had been previously covered with the usual dec present in such glaze compositions in order that orative glaze. Among the lead-free glazes known the desired low fusion or maturing temperatures to the ceramic arts before my discovery are many might be secured. As a result the glazes have china glazes which nature to decorative coatings been more or less soluble in various liquids such at relatively elevated temperatures, such as 1100 as fruit acids, and when the decorated ware has 20 to 1300° C. Many sheet steel enamels now used been used for holding food this lead for decorating sheet metal surfaces do not cOn has constituted a menace to health. Moreover, tain of lead, but these enamels mature it has been very difficult to secure a glaze having attemperatures of about 800° C., which tempera satisfactory expansion characteristics when lead tures are very close to the upper end of the china, Oxide is present in such artglaze compositions. . 25 decorating maturing temperature range. More Artglazes which do not craze immediately after over, these sheet steel enamels craze and chip firing, or on ageing, have, in the past, had such off to a very serious extent if applied to china or inconveniently high fusion temperatures as to pottery bases. prevent their practical utilization in overglazing While many artglaze fluxes and overglaze bisque ware. In commercial pottery manufac 30 fluxes are to some extent interchangeable be turing the kilns are ordinarily operated only at cause they mature within substantially the same three temperatures: the temperature of bisque temperature range, the properties of fluxes uti firing; the temperature of glaze firing; and the lized for artglaze decorative purposes ordinarily temperature of decorating or overglaze firing. differ somewhat from those of flux compositions - The use for decorative purposes of glaze com employed in overglaze decoration. Any sub positions maturing at temperatures other than . stantial difference between the coefficient of ex those within the ranges of the three types of pansion of the flux composition and the coeffi kilns has been exceedingly inconvenient and im cient of expansion of the bisque is more likely to practical, especially in large scale manufacturing result in crazing when the material is fired di operations. Another disadvantage of artglazes 0 rectly on the bisque than when a layer of glaze as previously known to the art has been the low intervenes. For this reason the coefficient of resistance of the decorative surface coating to expansion of glaze compositions utilized as art abrasion or scratching. - glazes is more critical and must correspond more ... It is principally because of the above disad closely to that of the bisque than is necessary Vantages that the artglazes are not now in wide 5 in the case of compositions used for overglazing. use in the manufacture of ceramic ware. At The improved glazes maturing at a relatively low present the use of artglazes is restricted prin temperature with which this invention is con cipally to the production of decorative coatings Cerned may be used both as artglazes, and as of certain hues which cannot be produced at all Overglazes for decorating ware which has already With Ordinary glazes since the pigments are not 50 been preliminarily coated with a vitreous glaze stable at the higher temperatures used to mature composition. Such regular glazes. Among such hues are the I have found that a lead-free flux composition various hues of red produced by the presence of having the improved properties specified must cadmium pigments such as the various cadmium contain the oxides of the elements , , SulfoSelenide pigments in the glaze composition. 55 aluminum, and , and at least one of the Accordingly, it is one of the objects of this alkali metal oxides of the group including invention to prepare improved artglaze composi Oxide and oxide. Moreover, these ox. tions which can be applied to the bisque ware at ides must be present in the flux composition the low temperatures used for overglazing but within certain relatively narrow percentage which glaze compositions are free from lead com 60 ranges, which ranges may be specified as follows: pounds. The resulting decorative surface coat ing on the bisque ware thus introduces no prob Per cent lem when the ware is utilized for holding food Silica, SiO2------40 to 60 stuffs. Another object of this invention is the Boric oxide, BaO3-...------20 to 40 preparation of an improved artglaze, maturing Aluminum oxide, AlaC3------5 to 15 in the ordinary decorating temperature range, 65 , Li2O------1 to 2.5 which composition will not devitrify, chip or craze Potassium oxide or (KO immediately after firing or upon ageing, even Or Na2O); or a mixture of the two under those circumstances where the glaze is alkali metal oxides (K2O and (Na2O)- 2 to 6 applied directly to commercial bisque bodies 70 These percentages are by weight, based on the without intermediate glazing. Still another ob total weight of the flux composition. ject of this invention is the production of art The oxides listed in the above table may be re glazes of Satisfactory resistance to the action of garded as the essential elements, and must be acids and of high resistance to abrasive action. present in the flux composition in the amounts These and still other objects of my invention 75 therein specified. However, other additionalee 2,278,867 3 ments may be present in minor amount, and in artglazing or overglazing, thus differ markedly many instances it may be desirable to incorporate from most of the glass and pottery glazes now such additional ingredients in order to secure known to the art in that they are characterized special effects or improved properties. For ex by a high content of boric oxide. As they do not ample, a few percent of , CdC), include either oxides of lead or of the alkaline amounts ranging from 2% to 7% of the total metals they are thus distinguished from composition being suitable, may be included in all glass compositions and from the various the flux composition for the purpose of improving glazes of this type now known to the art. They the stability of colors resulting from the inclu may be distinguished from all glass enamels and sion of cadmium sulfide and of the cadmium sul 10 from the usual artglaze and overglaze fluxes as foSelenides in the flux composition. now known to the ceramic art by their high con oxide in Small quantity, amounts comprising tent of alumina, as well as by their freedom from from 1 to 7% by weight of the flux composition lead oxide. In spite of the high content of boric being suitable, may also be added to the batch oxide, and high ratio of boric oxide to silica in composition and melted into clear and homo 15 my improved glaze compositions, they are re geneous solution for the purpose of improving markably resistant to the action of acids. It is the resistance of the resulting glaze composition even more surprising that they possess fusion to the action of alkalies. Glazes including zir temperatures sufficiently low to permit them to conium oxide melted into the flux composition. mature in the overglazing range, and that this are described in my Copending application Serial 20 low maturing temperature is secured concomi No. 141,188, filed May 6, 1937. tantly with a low coefficient of expansion, since The flux composition may, also contain my improved flux compositions do not contain oxide, present to the extent of a few percent, by lead. weight, based on the total weight of the com Some typical and preferred batch compositions position. Amounts up to about 5% by weight 25 suitable for preparing the improved glaze com may be present. The presence of in positions with which this invention is concerned the glaze serves to improve the brilliance and are give in Table I. These compositions are let gloss of the resulting decorative coating. In all tered A to E, and Table II lists calculated melted cases, however, the glaze composition must con compositions of the glazes produced by melting tain the oxides of aluminum, boron, silicon, 30 the batch compositions given in Table I. In lithium, and one or more of the oxides of the both tables the figures represent percent by alkali metals sodium and potassium, and these weight based on the total weight of the batch ingredients must be present in the above speci composition or total weight of the melted flux fied proportions. composition. The presence of lithium oxide melted into the 35 TABLE I glaze composition serves to reduce the melting Batch compositions suitable for preparing im- . point of the flux so that the resulting vitrifiable proved lead-free glazes composition matures at a relatively low fusion temperature. However, lithium oxide cannot be Comp. Comp. Comp. Comp. Comp. employed as the only in the 40 A. B C EP E. glaze composition, or devitrification during firing - Boric acid, HBO3------will occur to a deleterious extent. Either sodium Flint, SiO------32.2 32.2 25.6 34.6 oxide, Na2O, or potassium oxide, K2O, may be in Lithium carbonate, corporated with lithium oxide as the alkali metal LigCOs.------4.0 3.7 3.2 2.9 4.0 Kaolin, t oxides in the flux composition, but for best re Also.2SiO2HO ---- 13.2 1.5 14. 13. 26.7 , - sults it is preferred to have present the oxides of 2KCO.30------2. 2.5 : 5.0 ------4.0 all three alkali metals, i.e., lithium oxide, sodium Borax, NaBO.10HO- 6.6 8.3 ------11.8 ------Zinc oxide, ZnO----- 3.3 6.6 5.7 5.2 ------oxide, and potassium oxide, these oxides being Sodium zirconium sili present in approximately equal weight percents. cate, 14% NaO, 29% SiO, 55%. 2rO----- 2.0 2.5 2.1 .2.0------It has been observed that the oxides of the 50 Cadmium oxide, CdC). 3. ------alkaline earth metals, i. e., the oxides of the Sodium nitrate, NaNO------.. 4.0 metals , , , and , have detrimental properties when incor porated in the flux composition and interfere TABLE II . Seriously with the obtainment of the desired low Calculated compositions of improved lead-free maturing temperatures. For this reason my im gla2es' proved lead-free artglaze compositions, suitable - - Flux Flux Fixitxi Fuy also for use in overglazing, do not contain the r A B C D E

Oxides of the alkaline earth metals in any sub stantial amount. Under some circumstances, 27.0 23.8 31.6 36.0 9,3 50.3 5.8 46.0 43.8 6.3 however, amounts up to 4% may not be detri 2.1 1.9 J.7 1.6 2, 1 mental. 6.7 8.3 7.4 7.0 13.5 1.5 1.8 3.8 ------29 When the oxides specified and in the propor .8 2.2 0.4 3.0 9 tions stated are included in my improved glaze 4.2 84 7.6 7.1 - compositions it is noteworthy that these fluxes 1.4 1.8 1.5 1.5 ------When applied as artglazes to bisque bodies result. 5-0------in vitrified decorative coatings having substan In order to prepare the flux compositions of tially no tendency to devitrification. This sur Table II from the batch compositions of Table I, prising lack of tendency to devitrify is indeed re the ingredients necessary to make up the batch markable, as ordinarily the glazes which are free are carefully weighed out, and mixed thoroughly. from both lead oxide and the oxides of the alka The batch is then melted, preferably in a crucible line earth metals have a pronounced tendency or rotary furnace, at a temperature of 1200 to to devitrification which renders them unsatis 1300 C. until complete meiting occurs. Fusion factoryMy improved for commercial glaze compositions,glaze decorative suitable purposes. for 75 is continued until the melt is clear and trans 4 2,278,867 parent throughout. The exact conditions under The suspension of glaze in the aqueous vehicle which melting is carried out are not critical, nor was readily applied to the bisque to be coated by is it necessary to use the particular raw material dipping, but could also be applied by spraying or sources or chemical compounds given in Table I by any other suitable method. The ware was in order to introduce the ingredients present in then fired in the overglazing fire at a tempera. the calculated melted compositions given in Table ture of 700 to 800° C. The resulting product was II. Other suitable sources of the oxidic ingre ceramic ware coated with a red, glossy, decora dients of the flux may of course be utilized. After tive coating. The colored decorative coating melting, the melt can be conveniently fritted by had a high resistance to the action of acids, sat pouring it into water. . 20 isfactory resistance to abrasion, and there was In preparing colored-artglazes and overglazes no evidence of crazing or chipping anywhere on suitable for use in application to bisque ware, the the vitreous surface. flux composition is ground to a fine state of Sub division with a suitable ceramic pigment. The ExAEPLE 2 grinding is conveniently carried out in water, Flux B of Table II, having the calculated com acetone, or in any other liquid. The grinding position given in that table, was prepared from conditions are essentially the same as those en batch composition B of Table I. After the in ployed in grinding ordinary artglaze and over gredients comprising the batch composition were glaze colors, except that the period of grinding weighed out and thoroughly mixed, the batch was must ordinarily be about twice the length of time 20 melted in a rotary furnace at a temperature of now required to reduce the usual artglaze or - 1200 to i300° C. Melting was continued until overglaze to a similar state of fine subdivision. the melt was entirely clear and transparent. The The longer period is required to grind my in melted glaze composition was then poured into improved fluxes to an equal fineness because of . water in order to secure a fritted product in the their greater mechanical hardness and tough manner now well understood in the art. IeSS. To 93 parts of flux B of Table II there were When it is desired to pigment the improved added 6 parts of aluminate blue pigment fluxes with cadmium sulfoselenide red pigments and 1 part of oxide opacifier. The resulting it is preferable to grind the flux with the pig mixture was ground to a fine state of Subdivision ment, sinter the mixture, and then grind again. 30 in Water. It was then suitable for direct ap The sintering operation, which consists in bring plication to bisque ware for artglazing or as an . ing the fine color just to a condition of fusion in Overglaze. a furnace preferably held at a temperature with in the range 600 to 800° C., has the effect of aug The colored flux composition was suspended menting the brightness and stability of the re in water containing about 4% ammonium hy sulting red artglaze or overglaze. droxide (commercial solution of specific gravity As examples of my improved colored glaze 0.90) and 1% of casein. Bisque ware was then compositions, suitable for use as artglazes or as coated with the suspension of the glaze by spray overglazes, and as illustrative of the methods by ing the ware with the suspension. The product which these fluxes may be prepared, the follow was fired in the overglazing fire at a tempera ing may be given: , 40 ture of 700, to 800 C. and a blue vitrified decora tive surface coating was secured. The resulting EXAMPLE 1. coating had satisfactory resistance to abrasion A flux having the calculated composition given and was highly acid-resistant. The decorative for flux A in Table II was prepared from the coating was entirely free from crazing and chip batch ingredients tabulated under composition A ping, and since it contained no compound of in Table I. After thorough admixture of the lead, presented no danger to health even when . ingredients comprising the batch, the melt was the resulting article was used for holding food charged into a crucible and melted, a tempera products. ture of 1200 to 1300° C. being employed. Fusion It will be apparent that while I have described. was continued until the fused product was en certain improved embodiments of my improved tirely clear and transparent, The melt was then lead-free glaze compositions, suitable for use poured into water and fritted in the usual in artglazing or overglazing and applicable to lane. . . . - bisque at the usual temperature at which over 95 parts of the flux were then mixed with 5 glazing firing is carried out, many changes and parts of cadmium sulfoselenide red pigment. modification may be made in the preferred em The mixture was reduced to a fine state of sub bodiments disclosed without departing from the division by grinding in water, and then dried. It spirit or scope of my invention. Accordingly, the was then sintered at a temperature of 750° C. Scope of my invention is to be construed in ac The sintered enamel was crushed, reduced to a cordance with the prior art and appended claims, fine state of subdivision by grinding in acetone, and it is not to be restricted to the various condi-. and again dried. The resulting colored glaze tions and proportions referred to merely as illus composition was suitable for use in applying art Eve of preferred embodiments of my inven glazes or overglazes to bisque ceramic ware for O - w forming therein a red, glossy, decorative surface 65 claim: . . . coating. 1. A lead-free vitrifiable ceramic glaze com Bisque ware was coated with a suspension of position which comprises silica in amounts rang the fine artglaze in water. In preparing the SuS ing from 40-60%, boric oxide present in amounts pension of the glaze in water, 4% of ammonium ranging from 20-40%, aluminum oxide present hydroxide (commercial aqua ammonia solution 70 is amounts ranging from 5-15%, lithium oxide of specific gravity. 0.90), and 1% casein were first present in amounts ranging from 1-2.5%, and an added to the water in order to improve the work alkali metal oxide selected from the group which ing properties of the resulting suspension and to consists of sodium oxide and potassium oxide, retard settling out of the solid particles in the said alkali metal oxide being present in amounts . Suspension. 75 ranging from 2-6%, all percentages being by 2,278,867 v 5 weight based on the total weight of said glaze weight based on the total weight of said glaze composition. composition. 2. A pigmented lead-free ceramic glaze com 6. A lead-free vitrifiable ceramic glaze compo position, Suitable for use in Overglazing or as an sition which comprises silica present in amounts artglaze, which comprises a ceramic pigment and 5 ranging from 40-60%, boric oxide present in a fritted vitrifiable glaze. composition having the amounts ranging from 20-40%, aluminum ox following composition: silica in announts rang ide present in amounts ranging from 5-15%, ing from 40-60%, boric Oxide in amounts rang lithium oxide present in amounts ranging from ing from 20-40%, aluminum oxide in amounts 1-2.5%, an alkali metal oxide selected from the ranging from 5-15%, lithium oxide in amounts O group consisting of sodium oxide and potassium ranging from 1-2.5%, and an alkali metal oxide oxide in amounts ranging from 2-6% and zinc selected from the group which consists of sodium oxide in amounts ranging up to 5%, all parts oxide and potassium oxide in amounts ranging being by weight based on the total weight of from 2-6%, all parts being by Weight based on said glaze composition. the total weight of said fritted glaze composi 7. A lead-free vitrifiable ceramic glaze compo tion. sition which comprises silica present in amounts 3. A lead-free vitrifiable ceramic glaze com ranging from 40-60%, boric oxide present in position which comprises silica in amounts rang amounts ranging from 20-40%, aluminum oxide ing from 40-60%, boric oxide in amounts rang present in amounts ranging from 5-15%, lithium ing from 20-40%, aluminum oxide present in 20 oxide present in amounts ranging from 1-2.5%, amounts ranging from 5-15%, lithium oxide an alkali metal oxide selected from the group present in amounts ranging from 1-2.5%, an al which consists of sodium oxide and potassium kali metal oxide selected from the group con oxide in amounts ranging from 2-6% and zinc sisting of sodium oxide and potassium oxide in oxide present in amounts ranging up to 5%, all amounts ranging from 2-6%, and cadmium oxide 25 parts being by weight based on the total weight present in amounts sufficient to improve the sta of said glaze composition, alkaline earth metal bility of the color of the glaze composition re oxides being substantially completely absent from sulting when said vitrifiable composition is pig said glaze composition. mented by the addition of suitable ceramic pig 8. A lead-free vitrifiable ceramic glaze compo ments. 30 sition which comprises silica present in amounts 4. A lead-free vitrifiable ceramic composition ranging from 40-60%, boric oxide present in which comprises silica in amounts ranging from amounts ranging from 20-40%, aluminum oxide 40-60%, boric oxide in amounts ranging from . present in amounts ranging from 5-15%, lithium 20-40%, aluminum oxide in amounts ranging oxide present in amounts ranging from 1-2.5%, from 5-15%, lithium oxide in amounts ranging 25 an alkali metal oxide selected from the group from 1-2.5%, an alkali metal oxide selected from which consists of sodium oxide and potassium the group which consists of sodium oxide and oxide in amounts ranging from 2-6% and zinc potassium oxide in amounts ranging from 2-6%, oxide present in amounts ranging up to 5%, all zirconium oxide present in amounts ranging from parts being by weight based on the total weight 1-7%, said zirconium oxide being present dis 40 of said glaze composition, alkaline earth metal Solved in the glaze, all percentages being by oxides being present in amounts not exceeding weight based on the total weight of said glaze, 4% by weight of said glaze composition. composition. . . 9. A decorated ceramic article which comprises 5. A lead-free vitrifiable ceramic glaze compo a fired clay body decorated with a pigmented sition which comprises silica present in amounts 45 lead-free vitrifiable ceramic glaze composition ranging from 40-60%; boric oxide present in which comprises silica present in amounts rang amounts ranging from 20-40%, aluminum oxide fing from 40-60%, boric oxide present in amounts present in amounts ranging from 5-15%, lithium ranging from 20-40%, aluminum oxide present oxide present in amounts ranging from 1-2.5%, in amounts ranging from 5-15%, lithium oxide" an alkali metal oxide selected from the group 50 present in amounts ranging from 1-2.5%, and an which consists of sodium oxide and potassium alkali metal oxide selected from the group which oxide in amounts ranging from 2-6%, cadmium consists of sodium oxide and potassium oxide in oxide in amounts ranging from 2-7%, and a small amounts ranging from 26%, all percentages amount of a red ceramic pigment selected from being by weight based on the total weight of said the group which consists of cadmium sulphide 55 decorated glaze composition. and cadmium sulfoselenides, all parts being by ADEN J. DEYRUP.