| Gelatine | 2 | parts. |
| Water | 4 to 7 | " |
| Sugar[8] | ¾ to 1¼ | " |
[8] For some purposes (instead of sugar), glycerine, sugar of milk, or treacle may be substituted.
The pigments are made up into what are termed jelly colours, which are ground either by hand on a slab of glass, marble or granite, using a suitable muller for the purpose, or when large quantities are required a paint mill driven by steam or other power is employed. In hand grinding the colour is kept moist by syrup on greatly reduced stock jelly. After grinding by hand the pigment is lifted from the slab with a palette knife and stirred into melted stock jelly. When the mill is used, the pigment is mixed with the jelly before grinding. The proportion of pigment to jelly varies enormously according to the nature of the pigment, and may be anything between 2½ per cent. and 25 per cent. Having prepared stock jelly and jelly colours, and allowed both to set, they are weighed out in proper proportions, the jelly being dissolved in a tin vessel placed in a water bath. The colour, generally speaking, is dissolved in a small proportion of the stock jelly placed in the mill and again ground into the bulk of the jelly. In some cases the pigment is dissolved in warm water and filtered through cotton wool, fine felt or flannel. After adding powdered recrystallized bichromate, the jelly compound is ready for coating or spreading on the paper. The coating may be done by hand or machine. Several forms of machine are in use, including the first form invented by Mr. Swan. When only a small quantity is required, it is the general practice to coat by hand.
In hand coating, the tissue compound may be strained through fine muslin into a flat tin dish placed on a water bath; the surface cleared of air bubbles by dragging over it a strip of stiff paper. The sheet of paper to be coated is held in an upright position at the further end of the dish with its bottom edge just touching the surface of the solution, gently lowered until the whole surface of the sheet is in contact with the solution. If the lowering is properly done there will not be any default in contact, but if allowed to rest on the solution a few moments, the presence of air bubbles, if any, will be detected by the presence of little lumps on the back of the paper, these may be removed by raising a corner and touching the spots with a finger tip. The sheet is then raised with a rather slow and steady motion, allowed to drip, then clipped to a line by its top corners and left to dry in a warm dry room from which white light has been excluded. When this method of coating is adopted it is best to have the sheets of paper an inch longer than the dish; the blank edge prevents contamination of the fingers and distortion of the sheet caused by contraction in drying. Another method of hand-coating is to roll the sheet into a tube shape, placing the roll on the surface of the jelly compound one and a half inches from the top of the free end, raising with rather slow and steady motion as before. When the second method is chosen an oblong and somewhat deep dish will be found better than the flat shape; the flat dish may be used if tilted to give greater depth of solution in a corner.
AT THE FOUNTAIN.
J. W. WADE.
In the manufacture of tissues the greatest care must be taken to avoid over or long-continued heating of the gelatine solution. Either a too high temperature or a lower temperature, long continued, destroys the solution by rendering a considerable portion of it soluble in cold water and to a great degree reducing its gelatinous character.
The samples of gelatine used in tissue making are of two kinds, although both of good quality they differ in solubility, in hot weather a larger proportion of the "hard" sample is used, in cold weather vice versa.