Shellac Varnish, Barriers, and Burn-ins

MPF Conservation is a full-service company specializing in conservation, restoration and preservation of furnishings of upholstered and non-upholstered objects, textiles and interior architectural elements in the Western United States;; this page discusses shellac or spirit varnishes and burn-ins.

Right, using shellac on the
Hearst Castle Gothic Sofa.

On this page we will discuss the following:

  • Shellac (made with shellac flakes)
  • Barriers
  • “Burn-ins” (actually molten infills) and Infills

Shellac is secreted by lac bugs, and the natural color of the shellac is determined by the trees the lac bug was feasting upon. Once processed it is sold as dry flakes, shown below.

MPFC typically mixes fresh varnish for each project. Varnish needs to be fresh as old varnish losses its efficacy. Below, two shellacs created for the water damaged State of Washington Legislative Building Walls.

What do we do with old varnishes? Kate uses them in her artwork to shift color or to add a sealant to watercolors with no issues.

Right, Kremer’s Retouching Colors.

Varnishes and waxes can be infused with color outside the natural shellac and resin color derived from a specific species of plant. Finely ground pigmented powers or various brands of liquid dyes made for these applications all can be used to turn a natural varnish or wax into a bright colorful varnish or wax or simply enhance the original color slightly.

Dewaxed Garnet Shellac and Dewaxed Beige Shellac
from Vijay Vilji’s Shellac Finishes, above.


MPFC mixes its shellacs fresh from shellac flakes and lab grade isopropyl alcohol. We never ever purchase “shellac” from hardware stores because most of their shellacs are not pure shellac, but modern mixes which often result in detrimental effects on historic objects.

Shellac, unlike the tree resin varnish on the Oil Varnishes page, can be used it in a well-ventilated room without a ventilation mask. This is due to the less toxic nature of isopropyl alcohol as its carrier.

This is not true relative to some shellac varnishes created using methalated spirits. We rarely use these as they are created for a French polish which will “flash” or evaporate quickly, best used on fresh surfaces or surfaces which have been chemically stripped.

Right, several shellac varnishes mixed
from Vijay Vilji’s Shellac Finishes.

In most instances the color of the shellac comes from the choice of shellac flakes used, which in turn stems from the variety of the trees and bushes the beetles ingest. Color can also be influenced occasionally through the use of finely ground powdered pigments or liquid dyes infused into the shellac.

Barriers: When do we use them?

We do not use barriers with historic shellac amendments because when we work with fresh applications of true shellac (meaning the shellac we mix ourselves as described above, and not store bought with many additives) it binds with the historic shellac, producing a transparent warm finish.

Above and right, a sample drawer on the McLoughlin House Rosewood and Birds-eye Maple Wardrobe showing stages of restoration to the historic varnish surface before fresh applications:

  • The distressed historic varnish on a drawer in the base, image one;
  • The treatment halfway through finish reparation, second image;
  • And the completed drawer, third image right.

MPFC met our goal on the wardrobe finish, shown right: some craquelure is still visible as was intended, and after polishing, infill and wax, the drawer is vibrant.

When dyes or powdered pigments are used, such as the Kremer Violin Varnish Powders left, MPFC uses a barrier coat under the pigmented shellac.

Above, opaque sticks and hot melt lacquer sticks,
both used for “burn-ins”. Burn-in tools, below.

Burn-ins and Infills

“Burn-ins” (which are actually molten infills) can be created with either opaque or clear sticks, shown above, depending upon the object’s finish. The process uses specialized heated chisels (an example shown left), which takes a piece of the stick and as it melts leveling methods allow the melted stick to be placed into voids. These cosmetic infills can also include the introduction of textures and grain patterns to match surrounding areas.

However, infills happen in several ways beyond burn-ins.

Right, R&F Encaustic Paints is a wax-based “paint” we use for certain types of infills. Consisting of carnauba, beeswax, tree resin and pigments, they are applied into voids such as gouges or non-structural cracks. Because the texture of these area, which contain microscopic facets and protrusions which offer “tooth”, the molten material, once cooled, is secured.

From the R&F site: “The word ‘encaustic’ comes from the Greek word enkaiein, meaning to burn in, referring to the process of fusing the paint.”

For discussion on other types of finishes, visit the pages below: