It should be kept in bottles filled as full as possible, and the addition of a little carbolic or salicylic acid will help to preserve it; for without this it will keep only about ten or fourteen days, and when made with hot water about half that time* Powdered gum arabic should not be used.
Dextrine Solution. This can be made as follows : -
Pure white dextrine ... ... ... i oz.
Boiling distilled water ... ... ... 3 ozs.
Methylated spirit'............ oz.
Stir till dissolved, and strain through calico. It should show no sign of acidity when tested with litmus paper. India-rubber Solution.
Pure masticated rubber ... ...... 80 grs.
Chloroform or benzole ... ...... 8 ozs.
Digest till dissolved. Benzole is cheaper than chloroform, but the smell is rather unpleasant to some.
Gelatine. This, if properly made, is convenient and easy of application. The print can be mounted whilst still damp, and it can be shifted about on the mount, or any excess of mountant wiped off, without leaving any trace on the mount, even if highly enamelled. The following is a satisfactory method: - Soft gela-tine, 200 grs.: soak in distilled water (6 ozs.) for an hour. Dis-solve by the aid of a water bath, and add, in small quantities at a time, methylated spirit,ozs., stirring constantly; allow it to set. Should any spirit separate out, the mixture should be re-melted, and a little more water added. The product should be a pure milk-white firm jelly. A little carbolic acid may be added if desired. When required for use, melt by the aid of hot water or a water bath.
Liquid Glue. This is sometimes used, but as many different preparations are sold under this name, each sample should be tested for acidity, as some consist of gelatine dissolved in acetic acid, which would soon cause fading. Another kind which we have used, but cannot highly recommend, is prepared by dissolv-ing 120 grs. of shellac in 4 drms. of methylated spirit by the aid of heat. It is waterproof, but only available when the paper is thick, well sized, and impervious to a varnish-like material. Some adhesive mounts have been introduced into the market, which are rather convenient, although they are rather liable to stick together