The design and style of frames is very much linked with architecture and furniture styles. (Reference 1) As they have evolved, so too has framing. In earlier eras, paintings were often reframed to keep up with the latest style, and it was not uncommon to find paintings from one century framed in frames made in a completely different century. Frames often reflected the taste of the paintings owner and this mismatched framing continued into museums well into the modern day although museums are now making a conscious effort to match frames and paintings of similar centuries together.
Prior to the 17th century, frames weren't stamped by their creators, which contributed to the lack of study on framemaking as an art form. Thanks to the advent of stamping, collectors can distinguish between different types of frames and the artists that created them. Some of the most sophisticated frames came from Paris during the 18th century. Framemakers, or menuisiers, as they were known, would undergo nine years as an apprentice before being accepted into the framemakers guild. (Reference 1)
Solid carved frames were expensive, and so many early 18th century frames were decorated using papier-mâché, which was formed in molds and then affixed to the wooden frames themselves. (Reference 3) Papier-mâché was driven out by the introduction of "compo", a composite of whittling, glue, riesin and linseed oil, although it did make a comeback in the mid-19th century for a short time. (Reference 3) Compo frames were very delicate but had greater detail and ornamentation. (Reference 3)
18th-century frames also have strong rococo influences which help to identify them. (Reference 2) Pine and lime were the most popular woods used during this period, since they were soft and easy to carve. (Reference 3) 18th- and 19th-century frames are also easy to identify by their large gilded tops, which give a top heavy appearance to the paintings they frame. (Reference 4) While frames before the mid-17th century tended to be painted, 18th century frames were often covered with gold leaf, another identifying feature