Meet other collectors at antique shows, ask similar questions and learn what they know. Talk to dealers about furniture they've sold from the same manufacturer, what they think about the quality and how to identify pieces.
There's no shortage of resources, however, to help you learn about the company that made your favorite antique chair or table, what else it made and how to identify its work. Antique books and fellow collectors can provide a wealth of information. If you find a mark, you can look it up in one of various reference guides. The archives includes stories as far back as 1851, though you may have to pay to read some articles.
The mark on the bottom of the dishes helps provide the answers. Nevertheless, they are well drawn and there are very good descriptions. This makes it useful as a field reference.
I would note that the style and history overview is very brief, and the line drawings of the furniture, while useful as a quick visual aid, could have been more carefully done. But to get up close and discover where was it made, possible makers, era, etc. Each state almost has its unique way of making its claw and ball different.
It helps to show each era and how furniture changed with the era. As others have mentioned, it contains hand drawn pictures, not actual photos. There are also experts in the field (not myself unfortunately) and they often have forums where you can post your photo and see if someone can identify it. Is the antique furniture section also free?
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The reason is the blackened colour around the lettering showing that it was burnt in not carved. They may be stamped in a variety of ways and often in more than one place. Often you find quite crude marks impressed on earlier pieces of furniture. Can you identify this antique flea-market item?