My own experience is not singular in this respect, for Mr. Brashear relates a similar occurrence.

The silver film is not always of the same quality, and experiments are needed to get more information as to what determines the greater density and coherence of some films over others. I have had surfaces of glass silvered experimentally where the film would not wash off with any amount of wet rubbing, these mostly on surfaces that had been silvered many times. Probably the glass in this case was in the best state to receive the new deposit; certainly the condition of the surface does affect the coherence of the silver as well as the amount of the deposit, as judged by the way in which certain parts on a mirror that has been incompletely cleaned show that the deposition has begun long before other parts, necessarily resulting in an unequal thickness of film. With the most careful cleaning of a mirror I have often found that the first application did not succeed, but the second on the surface just cleaned off with nitric acid was all right. The nature of the liquid other than distilled water last in contact with the surface of the mirror seems to be the determining thing. - (Common.)

(N) Partially Resilvering Pier Glass

Remove the silvering from the injured part, clean the glass, form a wall of beeswax round the spot, pour on it some silver nitrate, and precipitate the silver by sugar, or oil of cloves and spirits of wine. This does not leave a white mark round the prepared place.

(O) Curved Glass

This is a French process, used not only for fiat surfaces, but also for those which are curved, or cut into patterns. Dissolve GOO gr. neutral silver nitrate in 1200 gr. distilled water, add 75 drops of a solution composed of 25 parts distilled water, 10 ammonia sesquicarbonate, and 10 ammonia, sp. gr. 0.980; add also 30 gr. ammonia, same sp. gr., and 1800 gr. alcohol, sp. gr. 0 85. When clear, the liquor is decanted or filtered, and mixture of equal parts alcohol and oil of cassia is added to the silver solution in the proportion of 1 of the oil of cassia to 15 of the silver solution; the mixture is agitated and left to settle, then filtered. Before pouring upon the glass surface, or into the glass vessel to be silvered, the solution is mixed with 1-78th its bulk of essence of cloves, 1 part oil of cloves, 3 parts alcohol. The glass is thoroughly cleaned, and the silver solution is applied and warmed to 100° F. for about 3 hours; the liquid is poured off, and the silver deposit is washed, dried, and varnished.

(P) Watch Glass

Take a solution of silver nitrate in a watch glass (1 gr. of the salt to 30 cc. water), add very dilute ammonia, drop by drop, until the precipitate formed is partially dissolved. Add a drop of a solution of sodium and hydrogen tartrate. The liquid will turn black and the silver will be deposited on the watch glass, forming a brilliant mirror-like coating. The watch glass should be imbedded in some sand, and the sand gently warmed.

(R) Glass Globes

Take 1/3 oz. clean lead, and melt it with an equal weight of pure tin; then immediately add 1/2 oz. bismuth, and carefully skim off the dross; remove the alloy from the fire, and before it grows cold add 5 oz. mercury, and stir the whole well together; then put the fluid amalgam into a clean glass, and it is fit for use. When this amalgam is used for silvering, let it be first strained through a linen rag; then gently pour some ounces thereof into the globe intended to be silvered; the alloy should be poured into the globe by means of a paper or glass funnel reaching almost to the bottom of the globe, to prevent it splashing the sides; the globe should be turned every way very slowly, to fasten the silvering.

(s) Make an alloy of 3 oz. lead, 2 oz. tin, and 5 oz. bismuth; put a portion of this alloy into the globe, and expose it to a gentle heat until the compound is melted; it melts at 197° F.; then by turning the globe slowly round an equal coating may be laid on, which, when cold, hardens and firmly adheres. This is one of the cheapest and most durable methods of silvering glass globes internally.

(t) Silver nitrate, 1 oz.; distilled water, 1 pint; strong liquor ammonia, sufficient quantity, added very gradually, to first precipitate and then redissolve the silver; then add honey, 1/4 oz. Put sufficient quantity of this solution in the globe, and then place the globe in a saucepan of water; boil it for 10-30 minutes, occasionally removing it to see the effect.