Silvering of Glass

Ralph E. DunbarNorth Dakota State College, Fargo. North Dakota

In the silvering of glass articles and surfaces, distilled water should be used inmaking all solutions and in washing all surfaces. The cleaning of the surface ofthe glass to be silvered is of prime importance. A satisfactory surface cannot pos-sibly be obtained if there is the slightest bit of grease on the glass. The surface ofthe glass can be advantageously cleaned by rubbing it with some fine moistferric oxide (rouge). The rouge is then washed off but the hands must not touchthe face of the glass. A small soft brush or tuft of cotton may be used in thisoperation.One gram of stannous chloride and 1 ml. of concentrated hydrochloric acid

is dissolved in 25 ml. of distilled water. This solution is then further diluted to375 ml. with distilled water. The surface of the glass which is to be plated is nowwashed with this diluted solution of stanneous chloride, again avoiding any con-tact of the hands with the surface to be plated. The glass surface is then againthoroughly washed with distilled water.Ten grams of silver nitrate is now dissolved in 10 ml. of concentrated am-

monium hydroxide (sp. gr. .90). This solution is then diluted with the additionof 160 ml. of distilled water, thoroughly stirred and filtered. This solution may bepreserved in a dark bottle for future use, and will be subsequently referred to assolution (A). Ten grams of potassium sodium tartrate (Rochell salt) is dissolvedin 160 ml. of distilled water, thoroughly stirred and filtered. This solution will besubsequently referred to as solution (B). To mix for silvering, equal volumes ofsolutions (A) and (B) are used and twice the combined volume of (A) and (B) ofdistilled water is added. The glass to be silvered, which must have been previ-ously cleaned, is now placed on a perfectly flat surface where dirt will not settle.The mixed solution is now poured upon the upper surface of the glass, capillaryattraction holding the solution on the surface and up to the very edge of theglass. Flasks, beakers and similar containers may be filled with the silvering solu-tion. The entire surface to be plated must be completely covered with the solu-tion at all times. No heating is required. On standing for an hour or so, the silverwill deposit on the glass producing the mirror. A second or third portion of thesilvering solution may be used to increase the amount of the deposition. How-ever, the surface must never be allowed to dry and should be completely coveredby the silvering solution during the entire process. These mixed silvering solu-tions of this type or their residues, when allowed to stand for long periods, havebeen known to explode with considerable violence, due to the formation of silvernitride. Due caution should, therefore, be exercised at all times in disposing ofresidues.In the mirror trade, after the silver is deposited on the glass, it is dried on a

hot table and the back is first painted with pure orange shellac made from puregrain alcohol and then painted with a special mirror paint to protect the silver-ing.

Stopcock GreaseRalph E. Dunbar

Ten parts of vaseline and 2 parts of white paraffin are melted together on anoil bath and then 1 part of pale crepe rubber, cut into small pieces, is added. Thewhole is heated (in a hood) and stirred until a smooth, homogeneous solution isobtained. When cool this preparation makes a satisfactory lubricant for glassstopcocks, desiccators, etc. The viscosity of the wax can be increased by theaddition of a greater percentage of rubber or decreased by increasing the propor-tion of vaseline. Pure gum rubber tubing or stoppers may be substituted for thecrepe rubber, when the latter is not available, without greatly decreasing thequality of the product.

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