HE answer to this question depends so largely on the individual conditions, that only very general suggestions may be given. We have already suggested the need of experimenting and accurately recording the results of using various kinds of glue. Once again, your dealer will give you good advice nine times out of ten – and your own experience should afford the most valuable check on his suggestions.
In general, the following glues are indicated:
Wood joints – High test hide glues. They make strong, firm joints, which is extremely important, as joints are subject to more or less tension; and they set rapidly.
Veneers – A moderately high test mixture of bone and sinew or bone and hide. The higher test glues set too quickly for this particular kind of work. If a spreading machine is used, avoid a glue that tends to foam. Sometimes foaming is caused by its spreading too fast. Overheating glue also tends to foam it. This can be overcome by the addition of sweet oil or vaseline, paraffine or wax candle, but it is objectionable when veneering. It is best to be sure you have a glue that will not foam. Your dealer can tell you what glue to use.
Sizing – Use a glue free from grease and foam and one that flows freely.
Paper Boxes – A quick-setting hide glue is indicated for setting-up. For covering, a lower test bone glue is preferred, as it does not set so quickly. Paper box manufacturers are troubled more or less with foaming glue and can use the remedy suggested in the paragraph on veneers, as this will not be objectionable in paper box work.
Belting and Other Leather Goods – Here the principal requirements are flexibility, resistance to moisture and tenacity. The higher test glues are generally preferred.
Bookbinding – For pasting covers, a low-grade bone glue answers all requirements sufficiently well. For rounding and backing, where strain is exerted, a high-grade bide glue should be used.
For Emery Purposes – Very high- grade glue that has been carefully prepared to eliminate all acids, alkalies and impurities. A good emery glue possesses superior water-absorbing qualities. To test a glue for emery purposes, soak an ounce in about five times its weight of water at room temperature for 48 hours. If at the end of the time the water shows discoloration, or if decomposition is evidenced by a disagreeable odor, the glue is not adapted to emery use; otherwise it may safely be used. Weigh glue after the operation, to get an idea of its water- taking properties.
HOW MUCH TO PAY FOR GLUE
While the high test glues cost more per pound, they go farther and do better work, except in cases when their quick- setting characteristics are an objection.
Row much you can afford to pay for your glue is a question that you must answer from your own observation and tabulation of results. In certain lines it would be foolish to use a high-grade glue, where the work would not benefit in proportion to the increased expenditure. Any attention given to the subject will be well repaid.
KEEP ACCURATE RECORDS
Always keep accurate records, and base your future purchases upon the demonstrated comparative results already attained by the various glues you have used in actual practice.
No glue is good to use unless properly prepared. A 16-cent glue may be reduced to the grade of an 8-cent glue by over-heating. The grade of the glue at the time it is used is the important thing.
Do not by faulty methods of preparation impair the working quality of your glue. A glue of moderate high grade properly prepared is better for practical purposes than a high-grade glue whose working quality has been destroyed by excessive or prolonged heating.
Sometimes it is desired to use glue with waterproof qualities. Glue is rendered practically waterproof by adding a small quantity (about 1%) of ammonium or potassium bichromate to the glue liquid. Upon hardening, the glue then becomes waterproof. Adding a small quantity of formaldehyde to the liquid glue will help it to resist the action of water after it has dried for some time.
Others suggest dissolving glue in an equal quantity of water and adding about as much linseed oil as water, with the aid of heat, until a jelly is formed. This mixture is said to be practically waterproof.
A patented process has recontly been put out for which the claim is made that it can be applied to any glue irrespective of grade or make, rendering it absolutely waterproof. The result is attained by mixing the glue with certain chemicals in specified proportions, and then adding a certain arribunt of formaldehyde. Any amount of glue can be treated and the process is said to be most effective.
Of recent years efforts have been made to find a substitute for animal glue. The effort has met with success to a certain extent for particular kinds of work. Probably the newest addition to the list of vegetable glues is the mineral glue-silicate of soda. Liquid silicates were first sold for the manufacture of soap. In recent years certain forms have been used for light adhesive paper work. It is used in places where glue is too slow setting.
QUICK SETTING GLUES
When a glue is desired to set very quickly the manufacturer can usually furnish glue with the setting qualities desired for the particular work in hand. If this cannot be done, for any reason, remember that the temperature of the glue is an important factor. A low temperature aids in quick setting. Some paper-box manufacturers have had successful results in quick setting by adding a small quantity of turpentine to the liquid glue. Some add silicate of soda.
Specially made glues are supplied by manufacturers for work in which flexibility is needed. An easy way to increase the flexible quality of glue is to add a little glycerine to the liquid glue.