Use a stock solution of silver nitrate of the strength of 25 grains to 1 ounce of distilled water: Take 2 drachms of silver nitrate stock solution and convert it to ammonia nitrate, by adding ammonia drop by drop until the precipitate is redissolved. Add 3 1/2 ounces of distilled water.
In another measure take 80 drops (approximately 74 minims) of 40 per cent formalin. Pour the solution of ammonio nitrate of silver into the measure containing the formalin, then back into the original measure, and finally into the dish containing the glass to be silvered. This should be done rapidly, and the dish containing the mirror well rocked until the silvering is complete, which may be ascertained by the precipitation of a black, flocculent deposit, and the clearing of the solution. The actual process of silvering takes about 2 minutes.
Cleanliness throughout is of the greatest importance. The vessels in which the solutions are mixed should be well rinsed with a solution of bichromate of potash and sulphuric acid, then washed out three or four times under the tap, and finally with distilled water. For cleansing, dip the glass for a short time in a solution of bichromate of potash, to which a little sulphuric acid is added. The glass is afterwards well rinsed for a minute or two under the tap, flooded with distilled water, and dried with a clean linen cloth. A little absolute alcohol is then rubbed on with a soft linen handkerchief, which is immediately rolled into a pad and used for well polishing the surface. The cleaning with alcohol is repeated to avoid risk of failure.
After the mirror has been silvered, hold it under the tap and allow water to flow over it for about 3 minutes. Rinse it with distilled water, and stand it up on edge on blotting paper. When it is quite dry take a pad of very soft wash-leather, spread a small quantity of finest opticians’ rouge on a sheet of clean glass, and well coat the pad with rouge by polishing the sheet of glass. A minute quantity of rouge is sufficient. Afterwards polish the mirror by gently rubbing the surface with the pad, using a circular stroke.
It will be seen that with this process it is unnecessary to suspend the mirror in the silvering solution, as usually recommended. The mirror is laid in the dish, which is a distinct advantage, as the progress of the silvering may be watched until complete. The film also is much more robust than that obtained by the older methods.
II.—Clean the bare portion of the glass by rubbing it gently with fine cotton, taking care to remove any trace of dust and grease. If this cleaning be not done very carefully, defects will appear around the place repaired. With the point of a penknife cut upon the back of another looking glass around a portion of the silvering of the required form, but a little larger. Upon it place a small drop of mercury; a drop the size of a pin’s head will be sufficient for a surface equal to the size of the nail. The mercury spreads immediately, penetrates the amalgam to where it was cut off with the knife, and the required piece may be now lifted and removed to the place to be repaired. This is the most difficult part of the operation. Then press lightly the renewed portion with cotton; it hardens almost immediately, and the glass presents the same appearance.
Clouding Of Mouth Mirrors.
Magic Mirrors.
The cast disk of bronze should be turned up level on both sides, and the edges should be turned or shaped up, the metal being about half an inch thick. On the side which was at the bottom in casting, a line should be drawn to allow for working up the border or frame of the mirror, and on the rest of the smooth surface the design should be drawn, not having too much detail. It is best to mark the lines with a sharp scriber, to prevent their effacement during working. When the disk is marked out, it should be laid on a smoothly planed iron block, and the lines punched to a depth of about 1/4 inch, a punch with round edges being used. Then the disk should be turned down to just below the surface of the punched-in metal, and the border or edge formed, finishing smoothly, but without burnishing. The back can be turned down and, with the outer edge, burnished; but the inside of the edge and the face of the mirror should be polished with fine abrasive powder, and finished with fine rouge. When dry, the mirror will appear equally bright all over; but when breathed on the design will show, again disappearing as the moisture is removed. The metal punched in will be more dense than the rest of the surface, and will also be very slightly raised, this being imperceptible unless the polishing has been too long continued.
With iron mirrors a good mottled iron must be used, selecting hematite for preference; but in any case it must be chillable metal. Preferably it should be melted in a crucible, as this causes the least change in the metallic content, and as the metal can be made hot and fluid, it works well. The design must be worked out in iron of about 1/8 inch in thickness, and must be level, as it has to touch the molten metal in the bottom of the mold. If preferred, the design may be cast and ground flat, but this depends largely on the design. The chill pattern should be coated with plumbago, and in molding the disk pattern of about 1/4 inch in thickness should be laid on a board, and on this the design—chill—should be placed, and the mold should be rammed up from the back in the ordinary manner. The casting should be allowed to get cold in the mold, and should then be removed and dressed in the usual way. It should then be ground bright all over on emery wheels of successively finer grades, and the mirror surface should be buffed and polished until a steely mirror surface is produced. With a good mottled iron the chilled design will not show until the surface is breathed on or rubbed with a greasy rag, but will then show clearly.