To prepare the Silvering Solutions—make 3 standard solutions as follows—
| No. 1.{ | Nitrate Silver in crystals | 100 | grains. |
| Distilled water | 4 | oz. | |
| No. 2.{ | Potash pure by alcohol | 1 | oz. |
| Distilled water | 25 | oz. | |
| No. 3.{ | Powdered sugar of milk | 1/2 | oz. |
| Distilled water | 4 | oz. |
Solution No. 3 must be made just before using. The others will keep if the distilled water employed in their preparation is pure, and the solutions, when made, are kept in glass stoppered bottles.
Suppose it is desired to silver an 8-1/2 inch mirror, proceed as follows:—the total amount of solution required having been ascertained, as before described, pour 2 ozs. of solution No. 1 into the mixing vessel previously well washed and rinsed with distilled water, and cautiously add Liquor Ammoniæ. A grey precipitate will be formed; continue to add the ammonia, drop by drop, till the precipitate is just dissolved and the solution becomes clear. The solution should be well stirred with a glass rod whilst adding the ammonia. Now add 4 oz. of solution No. 2, and re-dissolve the brown precipitate which is produced with Liquor Ammoniæ as before described. There will now be about 6-1/2 oz. of solution. Subtract the 6-1/2 oz. from the total amount previously ascertained to be required, and the remainder will be the amount of distilled water to be added. Add half this quantity of distilled water to the 6-1/2 oz. of solution, and add a drop at a time of solution No. 1, till there is a slight precipitate, which cannot be re-dissolved by a considerable amount of stirring (say for 2 or 3 minutes); then add the remaining half of distilled water and cover up from dust the vessel containing the solution, so as to allow the slight precipitate to settle. There is a point of importance to be attended to, namely, that no more ammonia is employed than is absolutely necessary. The total amount of ammonia required in the 6-1/2 oz. of solution is about 2 drs.
To Clean the Mirror.
Fill the end of a test tube with cotton wool, leaving plenty outside the tube. Having poured a small quantity of strong nitric acid on the front of the mirror, rub the acid well all over the front and sides with the cotton wool brush. Place the speculum under a water tap for a few minutes till the acid is washed away, and finally well rinse with distilled water; then place it in the silvering vessel (previously thoroughly cleansed) and pour in distilled water till it reaches 1/8 inch up the side of the speculum.
To Mix the Solutions.
The precipitate having settled, pour into a clean vessel all that is clear of the solution, leaving about 2 oz. behind, which will be turbid with the precipitate, and therefore useless. The total amount will be afterwards made correct by the addition of the same quantity of solution No. 3. Having filtered solution No. 3, warm it to about 100° F. by allowing the bottle to stand in warm water, or by heating in a small flask. When everything is quite ready, add 2 oz. of the filtered solution No. 3, whilst warm, to the clear solution described above, and thoroughly mix.
To immerse the Mirror.
Remove the mirror from the distilled water, taking care not to touch the surface of the mirror, and wipe the back and edge with some clean cotton wool. If this precaution is not taken the water is liable to drain down the sides of the mirror whilst silvering, and cause streaks at the edge of the film. Having poured away the distilled water in the silvering vessel, substitute the mixed solutions, and directly the solution becomes slightly inky, gently immerse the mirror, taking care that no air bubbles, or specks of any kind, remain between the surface of the mirror and the solution. The mirror should not be removed from the bath until all the silver has been exhausted from the solution. This may be known by the solution being clear below the silver film on the surface of the liquid. The time required will vary from 45 minutes on a hot summer’s day, to 90 minutes when the thermometer shows a low degree of temperature. In the latter case it is better to have the silvering bath in a warm room.