What's the difference between a tazza and a comport?

Nothing, in practice. Both describe a shallow dish raised on a foot, and dealers use whichever word suits the piece. Compote, pedestal dish and cake stand cover the same form again. The naming follows trade habit rather than any difference in the object.

Are these mostly ceramic?

Yes. Porcelain leads the titles, and the remainder runs through pottery, majolica, ironstone, terracotta and stoneware. Metal turns up as ormolu mounts, gilt-bronze, pewter feet or enamel rather than as the body. Only two pieces in the whole archive sit outside ceramics: a pair in carved wood and a grisaille enamel tazza with a painted portrait.

How old are the ones for sale?

The dated field runs from 1800 to 1920, and nothing on record is earlier than 1800. Half the archive is placed only as "19th Century", which outnumbers every specific decade put together. Where a clean year is given, the 1880s and the 1920s are the two clusters, and "Victorian" and "Edwardian" get used as period labels rather than dates.

Do tazzas come in pairs?

Often enough. Pairs appear at least five times across the archive, and there is a set of three lattice bowls as well. Single pieces still outnumber pairs and sets. Pairs and larger sizes tend to sit in the upper half of the range.

Can a tazza be part of a service?

Sometimes. Two listings sell one inside something larger, a dessert service in one case and a fourteen-piece coffee service in the other. That's the exception. The form was a standard part of 18th and 19th-century dessert services, but pieces reach the market on their own far more often than complete.

How many turn up on Sellingantiques?

Around five a year, which makes this a small category. Twenty-eight different dealers have carried one across thirty-nine listings, close to a listing per dealer. No single dealer stocks them, so each one is a one-off arrival rather than something drawn from a standing shelf.