Richard JagelsThe tea caddy on the left is an example of Japanese lacquer work in which a dye and gold particles have been added. On the right are dewaxed garnet lac flakes. Dissolved in alcohol, they produce amber shellac. “Blond” flakes produce a lighter-colored finish. Because mixed shellac has a shelf life of six to nine months, preparing your own alcohol-based solution from lac flakes guarantees freshness.
A couple of old yacht tenders built by George Lawley & Sons recently caught the attention of Harry Bryan (WB No. 303) and Tom Jackson in his Currents section (WB No. 305). Part of the discussion centered on the aging interior clear finish on these two Lawley tenders. Bryan’s boat was built in 1925, while the one Tom reported on was built in 1913. In each case, the tenders predate the earliest synthetic finishes, which consisted of nitrocellulose lacquers, that came to market in the 1930s and ’40s. Bryan suggested that the Lawley he examined might have been finished with shellac.
This got me to thinking about the history of wood varnishes and what options were available to boatbuilders in past centuries. My research revealed, as might be expected, that for many centuries wooden boats, like barns and houses, were left unfinished. Only in the past few centuries were finishes regularly applied to watercraft.
Asian Prototypes
In China and Japan, household wooden items were coated with the resin from the lacquer tree (Toxicodendron vernicifluum) as far back as 5000 to 4500 B.C., as dated from archaeological sites. Dyes and introduced metal powders, such as gold or silver, were often added to the resin for decorative value; this ancient craft continues today (see photo above). The process is very labor-intensive, involving the application of tens or even hundreds of layers.
Another resin, derived from a few tree species cultivated in India and Thailand, is one harvested by an insect, Kerria lacca. This insect deposits extruded resin on tree bark, which can then be scraped off the branches. After laborious processing, pure lac flakes are produced, and when these are dissolved in alcohol: violà! shellac varnish. Between 50,000 and 300,000 lac insects are required to produce 1kg (2.2 lbs) of lac flakes.
An English writer sent to India in the early 1590s saw shellac resin blocks used to burnish wood turnings while the wood was spinning on the lathe. He observed: “it shineth like glasse.” But it was not until the British East India Company took control of the country from 1757 to 1857 that steps were taken to develop an export trade in lac flakes to the West. By the early 1800s, shellac was rapidly becoming the major varnish used for interior woodwork and furniture, and it remained so until well into the 20th century.
But Boats?
While shellac became the major interior wood finish of the 19th and 20th centuries, I wondered whether shellac found much use in boats. The major clear finish used on boats of this period seems to have been a mixture of pine tar, a by-product of charcoal production, and natural oils such as tung or linseed varieties dissolved in a solvent, usually turpentine. Stockholm tar was a common name applied to this mixture. Some tars were derived from woods other than pine. The British term for sailors, “tars,” relates to the frequency that this finish needed to be renewed on ships in the British navy. Stockholm tar was not only slathered on all the wooden parts of a ship, it also coated all the standing rigging; and, in Scandinavia, was often used to glue and waterproof riveted seams in hull planks.
Of course, one of the disadvantages of tar is the pungent odor—something British sailors carried with them whether on the high seas or on port leave. My guess is that shellac would have been preferred for pleasure yachts—certainly for interior spaces. Shellac may also have served as a prime coat for painted hulls. Even today, shellac is one of the best wood primers, particularly over resinous or oily woods. I have also seen historical references to using shellac as a glue to hold wooden plugs over countersunk screws in ships.
Shellac has had many historical uses, and even today it has industrial uses that surpass its value as a wood finish. Being nontoxic, shellac has wide applications in the food and pharmaceutical industries. Those shiny fruits and jelly beans in the grocery store often owe their luster to a thin coating of shellac. I know of two canoe builders in Maine who regularly apply several coats of shellac to the bottom of their canvas-covered wooden canoes. It acts as a wear layer to protect the canvas; it is also waterproof, easily repaired, and can be re-coated each season. I have used it on a fiberglass canoe for abrasion protection. Several coats can be applied in a single day.
Other Possibilities?
While shellac dominated the interior wood finish market in the United States from the late 1800s to the 1930s and beyond, it was not the only varnish available during that period. Two other tree-derived resins—amber and copal—were being combined with tung or linseed oil and a solvent-like turpentine to produce a varnish that became readily available in the United States in the late 19th and early 20th centuries. These varnishes, especially copal varnish, were prized for use on train and horse-drawn carriages. Copal and amber resins come in two forms: fresh exudation from trees or as fossilized resin. Baltic amber comes from European sources; copal is collected from Latin American trees or fossil mines. Fossil copal is harder than the fresh resin and was generally preferred, although many varnishes contained a mixture of the two. One reference compared shellac to copal-based varnishes and concluded that both were flexible and resistant to wear, but shellac tended to “chip or blanch” more than copal varnish.
While shellac or varnishes consisting of copal or amber could have been used on the Lawley tenders, another shipyard finish of that period was spar varnish. This yellowish, clear finish consisted of a “long oil,” generally boiled linseed oil, with a small amount of rosin. The rosin was derived from heating fresh coniferous resin, often pine, to vaporize its volatile components. The resulting rosin is semitransparent and varies in color from yellow to black. Of the three possibilities—shellac, copal or amber varnish, or spar varnish—the latter would have been the least expensive.
Spar varnish, with its high concentration of linseed oil, was flexible but did not produce a hard film surface like shellac or copal varnish. As such, it remained somewhat tacky and attracted dust and dirt particles, often turning quite dark over time. Since cost would not be the key factor for a yacht tender, shellac would likely have been preferred over spar varnish. One way of testing whether an old boat finish is shellac instead of varnish—whether spar, copal, or amber—is to rub a spot with alcohol to see whether it removes some of the finish. Shellac is alcohol-soluble, while the varnish varieties generally use turpentine as the solvent.
I would be remiss if I didn’t point out that modern spar varnishes resemble the original stuff in name only. Current spar varnishes are complex formulations of natural and synthetic resins, hardeners, ultraviolet-light-absorbing substances, and drying agents. While they can outperform older finishes, I still give shellac the highest marks as a wood primer. It will stick to just about any resinous or oily wood and provides high moisture exclusion, as confirmed by the U.S. Forest Products Laboratory. One or two coats dry quickly, preparing the surface for high-performance modern varnish topcoats. By choosing the right level of shellac processing, dewaxed flakes from dark garnet to light blond can be used to create the final hue of the varnished wood. Mixing your own shellac ensures freshness and establishes coating thickness. 
Dr. Richard Jagels is an emeritus professor of forest biology at the University of Maine, Orono. Please send correspondence to Dr. Jagels by mail to the care of WoodenBoat, or via e-mail to Senior Editor Tom Jackson, tom@woodenboat.com.