Here’s some tips in a 1925 home economics textbook for selecting canning jars, lids, and rings:
Glass jars rather than metal cans should be used for home canning. Jars should be constructed so that there is no contact of the fruit with the metal, hence a jar having a glass cover is desirable. A large opening, simple construction, ease in cleaning, and perfect sealing are characteristics of good fruit jars.
Glass jars should be tested before using. Partly fill the jar with water, adjust the rubber and cover, seal, invert the jar. Examine carefully for leakage.
Rubber Rings. – Soft, elastic rubbers should be chosen. It is poor economy to use old rubbers. Rubber after usage becomes hard and inelastic; it may cause imperfect sealing and hence decay of the fruit.
In certain processes of canning, it is necessary to subject the jars provided with rubber rings and covers to long periods of boiling or to the intense heat of a pressure or steam cooker. When such a method is followed it is especially necessary that rubber rings of good quality be used. To meet this requirement, the United States Department of Agriculture advises that rubber rings conform to the following:
- Inside diameter of 2 1/4 inches (for a jar of standard size).
- Width of ring or flange from 1/4 to 12/32 of an inch.
- Thickness of 1/12 of an inch.
- Tensile strength sufficient to “stretch considerably and return promptly to place without changing the inside diameter.”
- Firm enough so that no crease or break shows after it has been tightly folded.
School and Home Cooking (1925) by Carlotta C. Greer




