The plan I adopt is this,—I dissolve a large quantity of the
chemicals required in one-fourth or one-eighth the quantity of water
employed by Martin, so that in a Winchester quart stoppered bottle I
can keep a large supply ready. I make the silver and ammonia
solutions eight times the original strength, the potash and sugar
solutions four times only, as these latter solutions require more
water to properly prepare them.
Enough solutions to silver a 6-1/2 in. mirror, eight times are to be
made.
Dissolve 1400 grains of nitrate of silver in 10 ounces of water (it
may be clean fresh rain water filtered, if distilled is difficult to
obtain, and it will act very well), but do not put the silver into
the exact 10 ounces, but make up to exact 10 ounces after the silver
is dissolved. It is thus condensed eight times. Do the same with the
nitrate of ammonia, by dissolving 2096 grains.
Next prepare the potash and sugar solutions, condensed to four times
the initial strength.
Dissolve 8 ounces of potash, and make up to exactly 20 ounces of
water; if this is dissolved in a glass measure it will evolve
sufficient heat to break it; it is safely done in a clean white jug.
Lastly, dissolve 4 ounces of white sugar candy with 416 grains of
tartaric acid, and boil ten minutes in a clean glazed vessel; when
cold, add 8 ounces of alcohol, and make up to 20 ounces with water.
Do not use the solutions till all are of the same temperature, nor
on the same day as they are made; and do not silver until the glass,
and _everything_ used are of the same temperature. To insure this,
get the mirror ready and suspend in water, with the solutions all
collected in the room in which the silvering is to be done, and let
them remain until next day.
Now, remembering how many ounces were needed to leave one inch of
solution under the surface and a quarter of an inch up the sides of
the 6-1/2 in. mirror, using a vessel about 2 inches larger in
diameter than the mirror, pour into a glass measure 10 drams of the
silver solution, add next 10 drams of the ammonia, then 20 drams of
potash; if the potash turns the mixture thick, pour it backwards and
forwards into another vessel, or stir it with a strip of glass, or a
glass rod, for half a minute; if the mixture does not turn clear
(which it will not do if it has turned very thick on adding the
potash), add cautiously, drop by drop, some of the ammonia solution,
agitating it till it just clears; do not filter unless there are a
great many floating particles through using unfiltered water, the
floating particles cause minute black spots, which are, however, of
little consequence, as their action is only the loss of so much
light. Measure 20 drams of the sugar—and the mirror being ready to
dip (the amount with the sugar added must be the required quantity
previously ascertained), add the sugar, stir well, and immerse when
the mixture begins to turn dark ink colour.
When silvered, well wash the mirror with water of the _same_
temperature as itself (it may be safely sponged with a lump of
cotton wool), and stand it on its edge on blotting-paper to dry.
Drops of water standing long on it when drying will cause stains,
which will not readily polish off, and indeed these should not be
polished, as it is not right to polish one part more than another;
so it is best to leave them, or if this is objected to, re-silver
the mirror, when standing it in the sun and wind will soon dry the
surface, but be careful not to let the dust settle on it.
Do not warm anything; if the weather is cold, everything may be left
many hours in a warm room, but the _equal_ temperature is of the
utmost importance—the actual temperature is not of much consequence.
More failures are due to unequal temperature than any other cause in
the hands of the amateur. One careful and clever amateur informed me
that he had failed six times, but on the seventh, by attending to
the advice given above, the silvering was a perfect success, and all
seemed then as easy and certain as it had before seemed uncertain
and difficult.