Because different finishes have been used at different times, it’s often possible to date furniture simply by the finish on it.
In the 18th century and earlier, makers used whatever finish they had available, usually wax or linseed oil. If the maker lived near a port city, alcohol- or turpentine-soluble resins may have been available.
By the 1820s, transportation had improved and shellac flakes, along with other alcohol-soluble resins, became widely available. Alcohol evaporates rapidly so these finishes dry fast and don’t collect dust. As a result, shellac became the overwhelmingly dominant finish used on almost all furniture and woodwork for the next 100 years.
In the 1920s nitrocellulose lacquer became available and slowly replaced shellac as the favored finish. There were two primary reasons. First, shellac is a commodity product, so the higher the demand the higher the price. Second, in contrast to the single alcohol solvent required for shellac, lacquer thinner is a blend of many solvents with varying evaporation rates, so lacquer thinner can be adjusted so the lacquer dries at a normal rate in widely varying weather conditions.
By the 1960s, a number of additional resins had been developed, which began replacing lacquer. These include primarily very durable catalyzed, polyester and UV-cured finishes. In the amateur market, polyurethane varnish largely replaced alkyd varnish.
In the 1980s and 90s, water-based finishes were introduced to address the growing demand to reduce VOCs in coatings.
With this historical knowledge, and assuming you’re dealing with an original (not refinished) finish, you can fairly accurately establish the period during which the furniture was made by testing with various solvents using a process of elimination.
Wax dissolves in mineral spirits (paint thinner), naphtha and turpentine.
Shellac dissolves in alcohol.
Lacquer dissolves in lacquer thinner.
Water-based finish becomes soft and tacky in lacquer thinner, toluene and xylene.
Using one or more of these solvents, dab a little onto an inconspicuous area as shown in the accompanying picture of using denatured alcohol to test for shellac, and see what happens. If nothing happens with any of these solvents, the finish is varnish or one of the newer more-solvent-resistant finishes.
