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Photographic Notes. 
How to Make Ground-Glass.— Breaking the ground-glass is an 
accident not very easily remedied in a small country village where 
a new one cannot be procured. This is how I made one :— 
I bought five cents. worth of emery and two pieces of glass of 
the size required. Spoiled negatives will answer if they are 
cleaned, which can be done with a strong solution of lye. I 
placed one.of the glasses on a flat board, and sprinkled a small 
quantity of the emery on it, which I wet with water. Placing the 
other glass on that, I ground them together, renewing the emery 
and water whenever necessary. In about an hour, I had two of 
the finest quality of ground-glass fully as good as those I would 
have to pay seventy-five cents. for (size, 8 in. by 7 in.) The 
emery may be carried by the amateur much easier than an extra 
ground-glass.— Scientific American. 
Glass for Dark-Room Windows.— M. Scola has been trying a 
variety of experimental stains for the glass of dark-room windows, 
and has fixed upon the following formula :— 
Water safe 2 aoe! sLOOLG C: 
Gelatine ae sae .. 5 grammes. 
Nitrate of Silver si i etamme. 
Glass coated with this solution is exposed to light until it 
assumes a reddish-brown tint. It is then washed to eliminate the 
nitrate of silver. A surface is thus obtained through which the 
actinic rays do not pass. The colouration may be deepened by 
increasing the proportion of nitrate of silver up to 3 or even 4 
grammes. Glass tinted in this way may also be used to shade 
the dark-room lantern. 
‘Practical Hints. 
Violet Copying-Ink.—The following receipt is given for 
making violet copying-ink :— Dissolve 40 parts of extract of log- 
wood, 5 of oxalic acid, and 30 of sulphate of aluminium, without 
heat, in 800 parts of distilled water, and set aside for 24 hours. 
Next, raise the temperature to boiling-point in a bright copper 
boiler, and mix with it, while hot, 50 parts of wood vinegar. 
When cold, bottle it, and after a fortnight decant the liquid from 
the sediment. It writes a dark violet, and furnishes a bluish- 
violet copy. 
Wo 1906 I0—IO 
