Indelible India Ink.
Draughtsmen are aware that lines drawn on paper with good India ink well prepared cannot be washed out by mere sponging or washing. Now, however, it is proposed to take advantage of the fact that glue or gelatine, when mixed with bichromate of potassa, and exposed to the light, becomes insoluble, and thus renders India ink, which always contains a little gelatine, indelible. Reisenbichler, the discoverer, calls this kind of ink “Harttusche,” or “hard India ink.” It is made by adding to the common India ink of commerce about one per cent, in a very fine powder, of bichromate of potash. This must be mixed with the ink in a dry state; otherwise, it is said, the ink could not be easily ground in water. Those who cannot provide themselves with ink prepared as above in a cake, can use a dilute solution of bichromate of potash in rubbing up the ink. It answers the same purpose, though the ink should be used thick, so that the yellow salt will not spread.
To Make Copying Inks.
Dissolve in a pint and a half of writing ink (violet or any other color) an ounce of lump sugar or sugar candy. A copying ink, so slow drying that writing in it can be copied by the use of no greater pressure than the hand can produce when passed over a sheet of paper, may be made by boiling away nearly half of some ordinary writing fluid and then adding as much glycerine.
A Good Paster.
Let a little starch lie in vinegar over night. Pour in boiling water, stirring briskly till it thickens. It will keep better if a few drops of carbolic acid are added. A very little corrosive sublimate will keep out insects. A little glue dissolved in the vinegar will make it stronger. It leaves the pasted scrap-page flexible, adheres firmly, dries quickly, and does not give a varnishy look to even the thinnest print paper.
A Paste Which Will Not Spoil.
A paste that will not spoil is made by dissolving a piece of alum the size of a walnut in one pint of water. Add to this two tablespoonfuls flour made smooth with a little cold water, and a few drops of oil of cloves, putting the whole to a boil. Put up in a glass canning-jar.
Electric Paper.
Electric paper may be made thus:—Tissue paper or filtering paper is soaked in a mixture consisting of equal quantities of saltpetre and sulphuric acid. It is afterwards exposed to dry, when a pyroxyline (a substance resembling gun-cotton) forms. This is in the highest degree electrical.