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Hide Glue is often sold as granules and called 'scotch' or 'pearl glue.' It is an extremely strong, gap filling glue, which has the property of pulling surfaces together as it dries. It needs to be applied hot, and hardens as it cools. It has the great advantage over PVA that you can reheat it and the glue should re-melt, allowing you to remake joints or reposition veneer. If you want to use it as a gap filler you can mix in pigments to match the wood. The main draw back of this glue is that it is not weather proof, so for indoor work only.
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Here is an excerpt from the Carpenters, Joiners and Cabinetmakers & Guilders Companion on the subject of hide glue:
The quality of glue being of up most consequence to the woodworker, it may not be amiss in this place to say something respecting it, and the tests by which we may ascertain its adhesive properties, as by this means we may be enabled to select that which is best, as well as to reject that which does not possess the requisite qualities of adhesion and firmness, and first it may be observed that glue is made from either the skins or sinewy parts of animals, and also from the skins and some other parts of fishes, that of the eel and shark; that from animal substances is reckoned better than that from fishes; though the strongest glue perhaps, we are acquainted with, is isinglass, which is made from the air bladders of a species of large fish found in the Russian seas, but its great price makes it of little use to the joiner when other glue can be substituted; however, from chemical experiments that have been made, that glue which is manufactured from the skins of animals, is superior to that which is made from the other sinewy or horny parts of animals, and which is found by actual observation, in practice to be much superior to the glue made from the skins,and of fishes, as it is not so subject to be affected by the moisture of the atmosphere ; therefore the workman will always prefer animal glue to what is generally termed fish glue, but which latter is often sold as glue of the best quality; and here we shall endeavour, first to lay down some directions to choose this necessary cement for the joiner, and give such directions as shall enable the workman to form some estimate of its adhesive qualities; all glue in the cake is subject to the effect of the dryness or moisture of the atmosphere, becoming soft in damp weather, and crisp in dry; but the different kinds are differently affected, therefore it is best to purchase in dry weather, as that which is then soft is not of such good quality as that which is crisp, and if we hold a piece of glue up to the light, that which is the most transparent is in general the best ; and here it would be advisable before making a purchase, to submit to experiment a sample of the article which you wish to purchase: thus, if we take a cake of glue and cover it with water in a pan, and let it remain for two or three days, if it is good, it will not dissolve at all, but will swell by being laid in water ; whereas, that which is of inferior quality, will partly if not wholly dissolve in the water, for that which least dissolves is the best, or possesses superior qualities of adhesion, and will be least affected by damp or moisture; another test is, that being dissolved by means of heat in water, that glue is the best which seems most cohesive, or which is capable of being drawn out in thin filaments, and does not drop from the glue brush as water or oil would, but rather extends itself in threads when falling from the brush or stick, which, if the glue possesses the requisite properties, will be found to be always the case; these few hints, with a little experience, will enable the workman to judge of the quality, as well as the method of selecting that which is best calculated to ensure success with regard to the firmness and stability of our work. We may here add, that that glue which is made of the skins of old animals, is much stronger than that of young ones.