A glass jar with a screw top used to store home-made jams or other preserves. Jam is most often stored in jars that have a capacity of 450g.
Jam jar covers
There are two types of jam pot covers, one which is placed on top of the jam and one which covers the jar. Home-made jam should be topped with a circle of waxed paper, while the preserve is piping hot or completely cold, to help exclude air and prevent deterioration eg pot the jam and cover with a waxed disc.
When the jam is quite cold the jar should be topped with a damped cellophane round and secured with an elastic band, the cellophane will shrink when it dries to create a tight seal over the jar.