On Isinglass –
Fish glue is the best that one can use for gluing hard woods and metals. It is made with the skin, nervous and mucilaginous parts of certain large fish [sturgeon], which are found in the Russian seas. It is in the north where fish glue is made, from where the English and the Dutch bring it to us, especially from the Port of Archangel, where it is a good business. Good fish glue has hardly any odor, and should be of a white color, clear and transparent. One must pay attention that is not contaminated, that is, mixed of heterogeneous parts.
To make fish glue melt, you take it in the following manner: You begin by cutting the hard, dry glue in little pieces, then you put it in a clay pot or a glass vessel with good brandy, noting that the latter covers the glue. Then you bottle up the vessel, which one must fill only half full, and you put it all on hot cinders just until the glue dissolves perfectly. Or, you can cut the glue as above, and you soak it in the brandy until it has softened, then you make it melt in a double boiler, as is normally done.
There are workers who, instead of brandy, put the fish glue in ordinary water to which they add a garlic clove. This is rather good, but is not the same as brandy, to which one can add a bit of garlic, which can only augment the strength of the glue.
One can do the same thing with good English glue; that is to say, put [it] in brandy and garlic. I have done it many times, and that has always been successful for me.
— A.J. Roubo
