Earthenware glazes fire roughly between 1080 and 1180 degrees onto a body that stays porous underneath. That last point is what makes the glaze structural rather than decorative: on earthenware the glaze is the only thing keeping water out, so a craze or a chip matters far more than it would on stoneware.
The glaze is doing the sealing
A stoneware body is vitrified and holds water on its own. An earthenware body does not: fired at low temperature it remains absorbent, and if the glaze crazes, water travels through the cracks into the body. That is why crazing on earthenware is a functional fault rather than an aesthetic one, and why glaze fit deserves testing on this body more than on any other.
Why the colours are brighter
Lower temperatures preserve colourants that burn out or shift at stoneware heat, which is why traditional earthenware is associated with bright, clear colour and why maiolica and slipware traditions grew up on it. Reds, oranges and bright yellows are far easier to achieve at earthenware temperature than at stoneware, and that alone is a reason some potters stay with it.
Matching glaze and body properly
Use a glaze sold for the earthenware range, on an earthenware body, and test the pair. The boil-and-plunge test, where a fired tile goes from boiling water into cold, brings out a poor fit quickly. It is worth doing before a batch of functional work, because a crazing earthenware mug will absorb liquid and stain from the inside.
What it costs to fire
Less than stoneware, because the kiln is climbing to a lower temperature and holding for less time. Over many firings that is a real saving, and it is one of the practical arguments for earthenware in a school or a class, alongside the brighter palette and the shorter schedules.
Questions people ask about earthenware
Is earthenware glaze waterproof?
A well-fitted, uncrazed earthenware glaze keeps water out, and the body underneath is porous, so a craze or a chip lets liquid in.
Why are earthenware colours brighter?
Lower firing temperatures preserve colourants that burn out or shift at stoneware heat, particularly reds, oranges and bright yellows.
Can I fire earthenware glaze higher?
No. Past its range it will run off the pot and the body may bloat. Match the glaze range to the body and the kiln.