The best isinglass comes from Russia—the finest from Archangel; there are many spurious imitations manufactured in England—all more or less impossible to clarify: these kinds of isinglass are all more or less worthless, and are easily detected from their extreme whiteness, and fine, paper-like, shred appearance; while genuine isinglass, whether in sheets or shred, presents all the appearance of a dull, dingy, semi-opaque looking hard skin. The spurious isinglass is almost instantly dissolved by merely stirring it in boiling water, while genuine isinglass requires half an hour's gentle boiling to dissolve it.
When about to clarify isinglass, it is necessary—first, to cut it in shreds, and put it in a very clean stewpan,. in the proportion of an ounce of isinglass to half a pint of cold water; stir this on the fire until it boils, and then sot it down by the side to boil gently for half an hour; a few minutes before it is removed, add a lump of sugar, a teaspoonful of wood-vinegar, and a little cold water; stir all together, and remove the scum as it rises to the surface; and, at the end of the time, strain through a sieve, or napkin, for use.