Isinglass
3 of the 6 encyclopedias on this shelf carry an entry for Isinglass. All 3 are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
i'zin-glas, a particularly pure, transparent form of animal gelatine. The material is much the same as that of fish scales. The supply of isinglass is obtained chiefly from the air bladders of certain fishes. Formerly the sturgeons of the Caspian and Black Seas were the main source of supply, but Brazil, the East Indies, and the Hudson Bay country now furnish a part of the insinglass of commerce. The name has been applied popularly but incorrectly to the thin sheets of mica used for the panels of coal stoves, which resemble isinglass in appearance only. Isinglass panels would burn out instantly. Isinglass dissolves readily in hot water. In cookery, it is used to make jellies, blancmange, and to thicken soup. Being akin to glue, it is used in the manufacture of certain cements and court-plaster. It is employed as a sizing also to stiffen silks, gauze, and linen. See Sturgeon
The Encyclopedia of Founding (1892)
A very pure form of gelatine prepared from the entrails and air-bladders of fish, notably the sturgeon. It is semi-transparent when pure, and this may perhaps account for applying the name to the sheets of mica employed for sight-holes of cupolas, stoves, etc. Isinglass is an excellent material for making elastic moulds for obtaining plaster casts. See ELASTIC MOULDS. Isosceles Triangle is a triangle which has two equal sides.
Collier's New Encyclopedia (1921)
a very pure form of gelatine, e, prepared from certain parts of the entrails of several fish. The best is derived from the sturgeon, and is almost exclusively imported from Russia, twisted up in rolls or formed into cakes, which are afterward torn into shreds or cut into fine shavings. Good isinglass should be free from smell and taste, and perfectly soluble in boiling water.
What Has Changed in the Last Century
Aiton's 1910 note that the supply comes "chiefly from the air bladders of certain fishes," with Caspian and Black Sea sturgeon as the historic source, no longer holds: Caspian sturgeon are now protected under CITES and commercial isinglass is made largely from tropical fish and cod swim bladders. The cookery uses Aiton lists -- "jellies, blancmange, and to thicken soup" -- passed to cheap industrial gelatine made from cattle and pig hides and bones, and isinglass survives mainly as a fining agent that clears haze from cask beer and wine. That last use has become a public issue rather than a technical one: Guinness announced it would stop using isinglass so its stout could be called vegan, completing the switch in 2017. The mica confusion both Aiton and the 1892 Encyclopedia of Founding complain about has quietly settled itself, since coal stoves with mica windows are no longer household objects.
Written for this edition, 2026.