Tt the worker in wood, whether amateur or professional, as well as for ordinary domestic use, glue is such an in dispensable material that no apology need be offered for directing attention to it, though to many the subject may seem a somewhat profitless one. Unfortunately, though glue is in such constant use, its right preparation and application often receive insufficient care, especially at the hands of amateurs, whose work is confined principally to mending any little article that may have got broken. The thoughtlessness with which one so often sees glue used can only be because its proper manipulation is not properly understood.
First of all it goes without saying that there is more than one quality. Good glue can be had from any respectable dealer, but let us here utter a word of caution against low-priced glues: they are seldom to be depended upon, and the difference between top and bottom figures, is when one takes into account the long way a pound of glue will go in ordinary work, hardly worth consideration.
No glue enjoys a higher reputation than Scotch
and whew it can be obtained no trouble need be taken with other sorts. Some of the French glues are also very good, and pet hasp their light color and clearness may be tempting. It must not, however, be forgotten that, however useful a light colored glue may be for some purposes, it is often less tenacious than the darker kinds. The best glue is of a clear reddish-brown color, very perceptible when looked through, and free from creakiness and muddiness.
If on holding it up to the light it is cloudy instead of being clear, depend on it that the glue is not of the best. The dark, opaque-looking glue which one often sees in London shops, offered as “town made,” at ridiculously low prices, cannot be recommended. When broken, glue should present a clean, sharp fracture, but this is a test which can hardly he applied beforehand when purchasing only a small quantity, and, with other indications which to an expert may mean a good deal, can hardly be of much use to the novice.
He must be content to be guided to a great extent by the general appearance of the cakes, and a little comparison of different qualities which may come under his notice will soon enable him to distinguish them. They may now consider how to prepare, or as it is generally called “make,” the glue. It is presumed that the ordinary form of glue-pot, consisting of an outer pot to hold water only, and an inner one for the glue, is too well known to need any detailed description. In the absence of one of these, the glue may be made in an empty jam-jar, or anything of that kind; but on no account must the vessel containing the glue come in direct contact with the fire. If it does there is almost a certainty that the contents will be burnt, a risk that may be avoided by using a small saucepan as a substitute for the outer glue-pot.
For ordinary domestic use
A small glue-pot is preferable to a large one, or, at any rate, only a small quantity should be mixed at a time. The reason for this is that every time glue is melted it loses in strength, so that no more should be made at once than is likely to be soon consumed. However good the glue may be originally, by the time it has been several times melted it will have lost much of its virtue, and, so far as strength is concerned, be very inferior. To make the glue, break up a sufficient quantity into small pieces which will go conveniently to the bottom of the pot. It is not necessary to powder up the glue. Cover the pieces with cold water and let the whole stand for some hours. Do not use hot water in order to hasten the solution. Under the influence of the water the glue will swell and become soft; but please note that glue should not dissolve. It merely swells up and becomes soft.
The time required cannot be exactly stated, but if left in soak overnight it should be fit for use next morning. It may here be mentioned that one rough-and-ready way of recognizing the quality of glue is by noticing the quantity of water it absorbs. The more it takes the better it is ; but it is impossible to specify this test more exactly, and the hint is thrown out to direct the novice’s own observation. When the glue is soft enough, it only remains to dissolve it by heat, the outer pot being partially filled with water. In a short time the glue will have completely melted, and may possibly require the addition of some more water ; for it is a great and common mistake to suppose that the thicker the glue the better it holds. On the other hand, it does not do to have it too thin and watery. It ought to be thin enough, when quite hot, to run freely from a stick or brush dipped into it, much as ordinary paint or oil would, and thick enough when cold to form a tolerably firm jelly.
Unless it gelatinous when cold, it is too thin to be of use
as it is better for general work to have it too thick than too thin, water should only be added cautiously. A little from the outer pot can be poured in among the glue whenever evaporation may render this necessary. When the glue is hot, a very objectionable smell may sometimes arise from it ; but this smell must not be mistaken for the ordinary color of good glue, which, though very characteristic, can hardly be considered objectionable. We wish more particularly to direct attention to the peculiarly offensive odor of glue which has either been made from rotten material or has become putrid. Whichever it is, the glue must be condemned as being unmistakably bad, and in such cases the discovery cannot always be made till heat has been applied. As good glue also has an unpleasant color when burning, the novice should learn to recognize this, though, indeed, one can hardly be confused with the other.
Enough has now been probably said about the preparation of glue, though it may be well to add that if the contents be left for any considerable time the moisture evaporates, till a solid mass remains, as hard as the original cake. We now come to another part of the subject, the application of the glue; for, however carefully prepared and good this may be, the full benefit cannot be derived without care and some knowledge of the way in which it should be used. It may seem an easy matter to dab some glue on two pieces of wood and stick them together; but how is it one so often finds that breaks which have been mended at home are not effective?
The two pieces joined together come asunder again on the slightest provocation, just exactly at the joint. Now, unless the wood be of a very tough and strong kind, the glued joint ought to be at least as strong as the wood itself, i.e., the glue holds on so tenaciously that, as in the case of two boards of pine connected by their edges, an attempt to pull them apart would probably result in the split being in the solid wood in the direction of the grain, and not at the glued junction.
This leads us to say that two pieces of end-grain wood cannot be securely fastened with glue; hence the futility of any attempt to join such a thing as a broken chair-leg with it. Of course we refer merely to those instances where part of the leg is snapped off. If merely a piece is split away it is quite a different matter, for in this we have the fracture concurrent with the grain of the wood, and consequently there is a legitimate opportunity for glue. Whether for an original joint or a repair, however, the same general principles must be regarded where strength is an object. To begin with, the two pieces must fit each other exactly.
Glue will fill up any interstices there may be through clumsy fitting, but, though it fills them, it will not make by any means a strong joint. The two pieces to be united must be warmed where the glue is to be applied, so that the latter may not be chilled when it is rubbed on. It is possible to have the wood too hot; but this is a mishap which is not so likely to occur as having it too cold, as, by the time the wood is hot enough to injure the glue, it is almost burning, or at any rate scorching. So, perhaps, all that it can be necessary to say is this: Have the wood hot, but do not burn it. The glue itself being thoroughly hot, a small quantity must be rubbed on one of the edges, and not only on but well-into the wood. As quickly as possible the other edge, which is to be also warm, must be applied. When the edges are straight, instead of merely pressing them together it is better to slide and work them slightly against each other, as any air bubbles which may have formed between them are more certainly got rid of, as well as superfluous glue being squeezed out. This cannot, however, be managed when a break is being repaired, and direct pressure alone must do.
As much glue as possible should be pressed out
the closer the two pieces are brought together, in other words, the less glue there is between them, the better will be the result. No greater mistake can exist than to suppose a quantity of glue is required in the joint; nor is it enough just to press the two pieces together. The pressure must be main-tamed till the glue has thoroughly set or hardened, and the time for it to do so will depend on such a variety of circumstances that no details can be given beyond saying that a small joint left to dry Ma warm room should be sufficiently firm in a few hours. It may occasionally happen that a joint which has been glued once has come apart and requires rejoining.
Before this can be done the old glue must be thoroughly removed, and the same may be said even if the glue has only recently been put on, as, for example, when, through an error in supposing the joint to be firm before it is so, the pieces have been pulled apart. The glue which has exuded may easily be removed by a chisel when it has partially congealed, or even when it has become quite hard. As a rule, good glue is sufficiently tenacious for ordinary woodwork, but it may be strengthened by the admixture of a small quantity of brick dust or plaster of Paris. It is as well, however, to avoid adding anything unless absolutely necessary ; and as for the various recipes of which many have been published for keeping glue always ready for use in a liquid state, it may be said that none of them can be recommended where a strong joint is a primary consideration. Glue certainly may be kept liquid and not require heat to reduce to a usable consistency ; but convenience is attained at the expense of strength whenever this is the case. This remark does not apply to such glues as Le Page’s, which have deservedly become popular for domestic use, and no article on glue for household purposes could be complete without some reference to them.
That best known is Le Page’s, which is sold in bottles and tins in so many shops that it can hardly be looked on now as a novelty. Except in very cold weather, no preparation is necessary to render it usable, and, even in extreme cases, putting the tin or bottle in warm water will effect all that is required. There is practically no waste with the former, there is not so much difference from an economical standpoint as appears at first. As with ordinary glue, the great secret of success is not to leave too much in the joint. Perhaps it may be news to some that there is no better brush for gluing purposes than a piece of common cane, hammered at one end till the fibers are loosened and form a stiff brush. Before hammering, the hard outer coating of the cane should be removed.