Glue.—The best glue may be known by its paleness, but French glue is now manufactured of inferior quality, made pale by the use of acid, but which on boiling turns almost black. Good glue immersed in water for a day will not dissolve, but swell, while inferior will partly or wholly do so, according to quality.
In preparing glue, a few cakes should be broken into pieces and placed in water for twelve hours, then boiled and turned out into a pan to get cold; when cold, pieces may be cut out and placed in the glue-pot as wanted. This naturally refers to when large quantities are used, but small portions may be boiled in the glue-pot after soaking in water.
Glue loses a great deal of its strength by frequent re-melting. It should always be used as hot as possible.
Rice glue or paste.—By mixing rice flour intimately with |170| cold water, and then gently boiling it, a beautifully white and strong paste is made. It dries almost transparent, and is a most useful paste for fine or delicate work.
Paste.—For ordinary purposes paste consists simply of flour made into a thin cream with water and boiled. It then forms a stiffish mass, which may be diluted with water so as to bring it to any required condition. It is sometimes of advantage to add a little common glue to the paste. Where paste is kept for a long time, various ingredients may be added to prevent souring and moulding. A few cloves form perhaps the best preservative for small quantities; on the larger scale carbolic acid may be used; salicylic acid is also a good preservative, a few grains added to the freshly prepared paste will entirely prevent souring and moulding.
Paste is now made on a commercial scale by various Paste Cos., who send it out to all parts. The paste is exceedingly good, and keeps a long time.
Photographs.—A few words respecting the treatment of photographs may not be out of place here.
To remove a photograph from an old or dirty mount, the surplus of the mount should be cut away; it should then be put into a plate of cold water and be allowed to float off. A little warm water will assist in its coming away more easily, but should it not do so, the photograph has probably been mounted with a solution of india-rubber, and in that case, by holding it near the fire, the rubber will soften, and the print may easily be peeled off.
Very hot water is likely to set up a reaction if the prints were not well washed by the photographer when first sent out.
In mounting photographs, white boards should, as a rule, be avoided, because the colour of the boards is more pure than the lights of the photograph, and deaden the effect. A toned or tinted board is more suitable. |171|