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Patented Apr..1.2, I I v . a

' UNITED STATES PATENT yorncs

Albert Moore Barnes, Acton, London. England, as- ' > signer to Duro-Ray Limited; London, England, a British company ' a .- - ' NoDrawing. Application January '23, 1935, Se iisghNo. 3,143. Inqreat'Britain February 8, 10 Claims. ‘ (cl. 91-091) This invention concerns improvements in the changing temperature, must sooner or later gain manufacture of mirrors of glass or similar trans- access to the perforate silver ?lm and depreciate [parent or ‘translucent materials, particularly or destroy its light re?ecting value by oxidation mirrors for domestic and/or decorative purposes. ‘ and corrosion. Furthermore, from the imperfect It is common practice in glass silvering to make and partially crystalline perforate structure of 5 use of thevwell known silver ammonium tartrate the ?lm there is every likelihood of the ?lm, process in any one of its numerous modi?cations with its backing, stripping from the glass surface in order to produce the silver ?lm itself, and fur- owing to the lack of that intimate adhesion which ther to “back"_or protect the silver ?lm thereby is the property of silver solely in the colloidal‘ 10 formed by means of paints and varnishes which state. The loss .of light re?ecting value caused 10 may, if desired, contain such metals as aluminium by imperfections and extreme tenuity of silver in finely divided particle form, or by electro-p ?lms applied by thev silver ammonium tartrate depositing an extremely thin coating of copper processes is considerable and is commonly as much on to the silver ?lm, the thus applied copper coat- as 20% even in, good quality silvering. ing being further protected by the application of . It is a‘ desideratum to Provide mirrors Dartieu- l6 ' paints or varnishes, or again 'after applyinga coat- larly mirrors for domestic and/0r decorative ing of varnish to the copper surface to stretch purposes wherein the silver ?lms are sufficiently a thin sheet of lead over the varnished copper and dense, homogeneous and molecularly adherent to to press or roll it into good mechanical contact, the glass or similar transparent or translucent 2 O the lead providingthe metal protective backing, surfaces, wherein the light re?ecting properties 20 or alternatively to electro-deposit lead on-to the of the silver ?lms are at their maximum and copper for its better protection'against injury. wherein the silver ?lms are adequately protected None of these prior proposals when carried into ' against atmospheric and Other corrosion. me _ practice are entirely satisfactory ‘for mirrors, chanical abrasion. extreme variations in atmos 25 particularly mirrors for domestic and/or decora- Dherie temperature and. When used as a re- 25 tive purposes, the principal reason being. the lack ?ector of suitable curvature, against heat from of exact knowledge as to the formation and char- light sources suchas electric light or gas acteristics of the silver film itself and itsdeposi- . This desideratum is ful?lled in accordance with tion on the glass surfaces. Silver ?lms produced the present invention in which the process for 30 by the silver ammonium tartrate process. in any silvering glass 01‘ similar transparent or trans- 30 of its numerous modi?cations, are not only ex- lucent materials, particularly glass for domestic tremely tenuous but, owing to their imperfect. and/or decorative purposes. is characterized in “structure”, partially crystalline and pin-holey, that ?lms of colloidal silver only are formed to are more or less light absorbent and in part, or predetermined linear thicknesses on their surfaces ' 35 whole, do not adhere to the glass surfaces as‘ to facilitate the electro-deposition of metals for 35 intimately as they should. Thus, the silver ?lms Protective purposes- The application of this‘ or deposits, instead of being pure silver in the process to the manufacture of mirrors particularly colloidal state and as such devoid of structure and for domestic and/0r decorative purposes consists in molecular contact with, and positively ad- in eleetre-depesiting a coating of lead upon the 40 herent to the glass surfaces, are more or less mix- silver ?lm. _ " 40 tures of silver partly colloidal, but mainly crys- ' The conditions which should preferably be ob talline and further contaminated with silver in ' served in depositing the silver ?lm and in electro other states such as silver oxide. All or any of depositing the metal backing upon the silver ?lm the structural defects referred to above are likely will now be referred to. . 45 to become more pronounced during and after the The siivering Solutions Which. for convenience. 45 application of the various protective paint or other may be designated 8-1. and S2. l’or the silver solu backings. For example, granted the structural ' tions, and R- fer the reducing solution. may be defects referred to above, it is impracticable to considered to resemble those used ‘in the well close or cover up these defects by the chemical or known Brashier process for optical silvering. 5i) electro-depositlon of copper because the copper For instance the S.1.solution maybe compounded 50 surface must possess the same structure as, that by adding su?icient ammonium hydrate (NHiOH) of the silver ?lm on to which it has been deposited to silver nitrate (AgNOa) dissolved in distilled and When a paint or varnish is subsequently ap- water to convert the silver nitrate to silver oxide plied as 9' P1‘ Otecuve becklns» decommsmon Pmd' and to re-dissolve the precipitated silver oxide in . 55 uets Of these. under conditions of‘ moisture and an excess of ammonium hydrate. _ The 3.2. 5‘ 2 2,118,977 \ solution may consist of sodium hydrate (NaOHH) film of silver in‘ the colloidal state, adherent to dissolved in distilled water. Solution S2. is then and apparently'in molecular contact with the added to solution 3.1. and to the mixed 8.2. and glass or similar surface for example glass for 8.1. su?icient ammonium hydrate is added to re domestic and/or decorative purposes, has been dissoive any excess of silver oxide that may appear formed, the work is transferred to a bath, for as a precipitate after adding to 8.1., care being electro-depositing the lead backing. taken to avoid an excess oi.’ ammonium hydrate. This bath should be so constituted that the‘ The mixed 8.1. and 8.2. solutions are then diluted adhesion of the silver film to the glass is not ad with distilled water to a point when the original versely affected by the acid or alkaline reaction 10 silver nitrate content is ‘ approximately 5.00 of the electrolyte employed. The electrolyte 10 grams per litre, and the original sodium hy-' therefore is rendered as. nearly. neutral as may drate content is approximately 4.68 grams per be consistent with correct working. . ' ' litre; The R. solution may consist of cane sughr When electro-depositing lead a suitable elec and tartaric acid dissolved in su?icient distilled trolyte/consists of an aqueous solution of lead 16 water and in such proportion that it contains perchlorate Pb(ClO4)2. in which the lead con cane sugar 4.00 grams per litre and tartaric acid tent is 37.5 grams per litre, and the free vper 0.24 gram per litre. The solutions 8.1. and 5.2. chloric acid (H0104) content is 0.05%. Addi and the solution R. are purposely so compounded tion agents such as clove oil or peptone may be that equal volumes of solutions 8.1. and 8.2. and used to reduce the grain size of the deposited 20 R. react when issuing from their respective lead to the minimum. 20 nozzles referred to hereinafter and mix or mingle By the calculated composition of the lead-con to form a jet of mixed solution double the volume taining electrolyte, the disposition of the lead of the separate solutions, ‘(S.l.+S.2. and R.) and anodes towards the cathode, (the silver iilm in are purposely contrived to procure the exact con contact .with the glass or similar surfaces under 25 dition of silver deposit, only in the colloidal state, treatment), and the electric current employed 25 on the surface of the material under treatment for to complete the electro-deposition of the lead example glass for domestic and/or decorativepur-v backing, a dense, non-crystalline and homoge poses. neous coating of pure lead can be deposited on The vessels, one containing the mixed S.1.+S.2. every portion of the outer surface of the silver 80 solution and the other the R. solution are con ?lm in such a manner that it is encased with 30 veniently mounted at a suitable height above pure and ductile lead, to such a predetermined ‘the work to allow the solutions to be fed to the thickness as to afford protection againstme work. by gravity. Alternatively compressed air chanical injury, sea -air, damp and moisture, may be used for this purposeythe containing and most of the more injurious fumes and gases 85 vessels being kept at any convenient level. The likely to be encountered. Experience indicates 35 solutions for silverings S.1.+S.2. and R. are that a lead deposit 0.002 inch in linear thick caused to issue under the control of suitable ness is su?icient for this purpose but this thick valves or taps connected with the containers by ness can be varied in either direction by a simple suitable tubes or ducts. Each individual jet or time adjustment. 46 combination of jets consists of two separate noz The apparatus for carrying the process into 40 zles disposed towards each other at an angle of effect comprises: ' say 45°. Each jet consists of two nozzles, sep 1. Means to hold and secure the glass sheet arately connected, one to the solutions S.1.+S.2., in position during the silvering process and at the other to‘ the solution R. The solutions issuing the same time to impart motion, which may be from their respective nozzles, disposed towards circular, gyratory or reciprocating in a horizontal 45. each other at 45° are caused to mix at a calcu plane. Oneway for securing this is to attach a lated distance clear of the nozzles and by the ad vacuum plate or cup to the underside of the glass justed volume of the flow of the solutions, they sheet and by means of a spindle carrying'a ball become a single jet of mixed solutions double the which engages with a socket attached to the volume of the flow of the issue from the separate vacuum. cup to support the glass on a circular nozzles. At the point of the mingling of the two table attached to a supporting pedestal in such solutions, and by their calculated reaction when, a manner that it remains level or can be rotated mixed, the jet or jets of mingled solution become whilst level in a horizontal plane, or can be lifted actively silver depositing and when caused to by its spindle attached to the vacuum cup to a cu -vi flow over the glass or similar ‘surfaces under su?icient height above the circular table attached treatment deposit pure silver in the colloidal to the supporting pedestal so that resting in an state required, ?rstly as a slight discoloration or inclined position on the circular table the glass ?lm of silver in the colloidal state. This film is with the vacuum cup attached can be rotated rapidly built up by the constantly renewed ?ow at an angle inclined to the horizontal with a to of the mixed solutions which are only allowed to gyratory movement, or in any inclined plane de 60 remain on the surface of the glass or similar sired, for the purpose of creating the proper transparent or translucent substance for ex ?ow of the silvering solution over ‘the glass sur ample glass for domesticand/or decorative pur- ‘ face during the silvering process. poses whilst active in respect of the ?rst calcu Alternatively the glass may be mounted on a lated reaction and which drain off before de suitable supporting table, and whilst so supported, 65 positing silver in other states than the colloidal by mechanical means such as gimbals or a sys state required for the purpose in view. The proc- . tem of levers and pendulums the table supporting ess of depositing silver in the colloidal state call the glass sheet may be inclined at any desired ing for no particular skill on the part‘ of the oper angle to secure the desired flow of solutions over , 70 ator, is under perfect control, and the-building up and from the glass surface during the silvering to the required density is automatically governed operation. Trays or troughs can be arranged to by the time set for the operation, say from ten collect the spent solutions draining from the glass to ?fteen minutes in accordance with the den— during the silver-mg operation. The silvering, sity required. . _ conducted ‘at normal atmospheric temperature 75 After a su?iciently dense and homogeneous such as 65° F., does not call for the steam heated 3., tables employed in silvering by the silver am '7. A process for silvering glass and the like, monium 'tartrate ‘process. I ‘ comprising subjecting the glass to the action of’ '2. Means for electro-vdepositing pure metallic newly combined component silvering solutions for ‘ lead as a protective backing directly on to the such time as will cause the deposit thereon of silver ?lm previously deposited onto the glass sur only colloidal silver, draining the solution from face as described comprise a suitable tank or vat the glass before silver in other than colloidal form to. hold the electrolyte, lead anodes properly dis is deposited, repeating such sequence of deposit posed in relation to the silvered glass sheet to be ing and draining operations until the colloidal treated and a supporting frame to carry the sil silver deposit on'the glass is built up to a desired vered glass during the electro-deposition provided thickness, and electro-depositing a backing of 10 with contacts and electrical connections to couple lead on the colloidal silver deposit. L up the silver ?lm, acting now as the cathode in 8. A process for silvering glass and the like, the lead depositing process, to the source of elec comprising continuously combining separate tric supply. _ ' streams of component silvering solutions to form 15 The mirrors produced in accordance with this a stream of complete silvering solution, subject 15 invention consist primarily of a sheet of plane ing the glass- to the newly formed complete solu or curved glass or similar transparent or trans i'tion for ‘such time as will cause the deposit there lucent material, a ?hn of pure silver adherent to on of only colloidal silver, draining the solution and in apparent molecular contact with the glass from the glass before silver in other than colloidal 20 or similar transparent or translucent material form is deposited, repeating such sequence of de and purposely contrived to be su?iciently dense positing and draining operations until the col and homogeneous so as to render it totally or loidal silver deposit on the glass is built up to a 100% light re?ecting for the value of pure sil desired thickness, and electro-depositing a back ver as a light reflecting medium, and secondly ing of lead on the colloidal silver deposit. ,25 of a coating of pure lead incorporated and in 9. A process for. silvering glass and the like, 25 positive metallic contact with the underlying sil comprising preparing a solution ‘of silver nitrate ver ?lm.‘ This protective coating of pure lead ‘in water, adding ammonium hydrate to said solu is homogeneous and imperforate by reason of its, tion until a precipitate of silver oxide is formed, method of ‘application upon an imperforate silver adding an excess of ammonium hydrate to the so 80 ?lm produced as hereinbefore described and is » lution to dissolve the silver oxide, adding a so- v 30 calculated to protect permanently the silver ?lm ' lution of sodium hydrate to said solution, adding‘ against such corrosive agencies as sea-air, damp ammonium hydrate to the mixture to dissolve any and moisture and atmospheric and chemical silver oxide formed, mingling a stream of the mix fumes and gases. Since there is no place in the ture of solutions with a stream of reducing solu lead backing where moisture, fumes and gases tion of. cane sugar and tartaric acid in water, im 35 can attack the silver ?lm, its value, as the‘ most mediately ?owing said mingled streams of solu e?icient light re?ecting surface obtainable, is per tions over the glass to be silvered, draining the manently unimpaired by oxidation or corrosion mixture from the glass before silver in other than from any external or internal source. ' colloidal form is deposited, continuing to ?ow What I claim is: . - ' fresh portions of said solutions, immediately after 40 1. A process for the manufacture of mirrors mingling, over- said glass until a silver deposit of comprising the steps of forming a ?lm of colloidal desired density is obtained, and electro-deposit silver only to a predetermined linear thick ing a layer of lead directly on the silver deposit. ness on a surface of transparent material and 10. A process for silvering glass and the like, of electro-depositing on the silver ?lm a coating comprising preparing a solution of silver nitrate 45 of lead for protective purposes. in water, adding ammonium hydrate to said so 2. A ‘process for the manufacture of mirrors lution until a precipitate of silver oxide ‘is formed, comprising the steps of forming a ?lm of colloidal adding an excess of ammonium hydrate to these silver only to a predetermined linear thickness on lution to dissolve the silver oxide, adding a solu 50 a surface of translucent material and of electro ' tion of sodium hydrate to said solution, adding 60 depositing on the silver ?lm a coating of lead for ammonium hydrate to the mixture to dissolve any protective purposes. silver oxide formed, said mixed solutions having 3. A process for the manufacture of mirrors an original silver nitrate content of approximate comprising the steps of forming a ?lm of colloidal ly 5.00 grams per liter and an original sodium ‘silver only to a predetermined linear thickness on v hydrate content of approximately 4.68 grams per 55 a surface of glass and of electro-depositing on the liter, mingling a stream of the mixture of solu silver ?lm a coating of lead for protective pur tions with a stream of reducing solution of cane poses. . sugar and tartaric acid in water, said reducing so 4. As a new article of manufacture a mirror lution having a ‘cane sugar content of approxi consisting of transparent material, an adherent mately 4.00 grams per liter and a tartaric acid 80 ?lm ‘of silver ‘exclusively in the colloidal state content of approximately 0.24 gram per liter, im upon the surface of said material and a protec mediately ?owing said mingled streams of solu tive backing of electroédeposited lead upon the tions over the glass to be silvered, draining the silver ?lm. ' mixture from the glass before-silver in other than 5.v As a new article of manufacture a mirror colloidal form is deposited, continuing to. ?ow consisting of translucent material, an adherent fresh portions of said solutions, immediately after ?lm of silver exclusively in the colloidal state mingling, over said-glass for ten to ?fteen min upon the surface of said material and a protec utes, and electro-depositing a backing layer of tive backing of electro-deposited lead upon the lead on the silver deposit in an electrolyte con 70 silver ?lm. - sisting of an aqueous solution of lead perchlorate 70 6. As a new article of manufacture a mirror in which the lead content is approximately 37.5 consisting of glass, an adherent ?lm of silver ex gramsper liter and the freeperchloric acid con clusively in the colloidal state upon the glass and tent is approximately 0.05 %'. p . a protective backing of electro-vdeposited lead upon the silver ?lm. ' ALBERT MOORE BARNES. u 1