Tabletop Restoration: Impurities in Shellac and other Woes

by DKP

I am going to let you in on a little secret:  There really is a Shellac God.  He is a fickle god, a prankster, and loves to keep conservators up at night biting their nails.

Okay, so I have lost my mind a little.  On the other hand, sometimes the impurities buried deep in historic layers of shellac varnishes can feel like pranksters.  You think you have them under control then they raise up and cause you all kinds of problems.  We have experience, and we prepare for these things, but two pieces of furniture are more inclined  to impurities laying below the surface: dining table tops and vanities or ladies dresser tops.

Yesterday when I was praying again to the Shellac Gods to please, please, please let this coat be the end of a current shellac problem, it occurred to me that noone writes about failures.  The upside to discussing failures is twofold:

1)    People who want to learn to be conservators and traditional finish restoration experts will learn best from hearing about problems;
2)    When problems arise causing delays, uninformed clients tend to wonder if you know what you are doing, primarily because they have only been exposed to modern synthetic finishing products.
This article may help with both.

shellac bar

So here goes.  Failures, problems, warts, et all.  Starting with this innocent looking table, below.



Most furniture gets a fair share of abuse: store bought waxes and cleansers, alcohol, perfume, food, etc. But tabletops and the tops of vanities or dresser drawers are the two that seem to carry the most impurities buried deep into the shellac, and this accrues over time.  With tabletops it is the addition of foodstuffs and dirty hands; with vanities it is creams, perfumes and nail polish accouterments.  These are often not seen, and the clients may be fastidiious housekeepers, but it is the nature of a lifetime of living that these pieces end up with impurities that bury deep into the finish.

Unlike the modern topcoats which are impervious (and they have their downsides) antique traditional finishes tend to be more organic and are more open to the environment.  The upside is that they age beautifully, developing rich patinas which are highly prized.  The downside is that, over time, minute cracks add to impurities buried into the finish.  Once every 50 years, it is likely that these tops will needs some sort of restoration, and the impurities embedded within the varnish substrates may cause problems during the restoration process.

First, preparation: clean, study, and stabilize the historic tabletop varnish using traditional conservation techniques and materials as necessary.  (This is a long process in itself, and food for another time.)  Usually that takes care of most of the historic impurities.  However, at some point, additional top coats of traditional shellac are added to unify and protect the original antique finish.  On very damaged finishes, or when the top was not French polished to begin with, we brush shellac.

We make our own shellac from the freshest shellac flakes, and use lab grade isopropyl alcohol as the carrier.  (More on shellac in another blog post.)

However, having done everything right in preparation of the tabletop and creation of our new varnish, this table had the number one problem that causes us to use many  coats of shellac:  impurities rising through the chemical reaction of the new shellac hitting the old shellac and releasing undetectable impurities in the vintage coats.

It manifests like this:  I am technically proficient, and in the course of applying a 2-lb cut of shellac to body up, and my brush drags in certain areas of the tabletop.

impurities rising 2lb cut DSC08958_2

Yikes!  Fizzing or bubbles appear in the wet shellac, and there is no rhyme or reason.  Some parts of the table allow the liquid shellac to flow and self-level, some areas begin to clabber immediately.  I clean my brush frequently, yet the brush drags in areas.  I finished the coat and cry over the splotchy appearance, cursing the shellac gods for bringing this to my studio!   Then I mea culpa and promise to do all I must do to create a beautiful finish.

This will involve two changes: extensive spot sanding, and changing to a 1-lb cut.  The latter means that more shellac coats are necessary to build up the finish.

Days later when the poor coat dries, I sand.  Sanding is an art onto itself.  When I first skip-sand the top, I am able to see clearly all the parts that have bubbled.

Impurities arising

These parts need a patient and gentle hand to sand just enough so that the bubbles are gone, but not too much so that I am back down to the original coat.  I use 350-400 sandpaper, and use my fingers for a light touch instead of a block.  I can feel and see the changes as they occur, below.

Sanding Impurities

Sanding Impurities

Sanded Impurities

When I am almost done, I also feather out, always sanding with my whole arm in alignment with the grain, to work the edges smooth.

Feathering Out

Below is the table sanded from the impurities, and the pattern supports the story of how the table was used.  The side toward the window is on the right, and was not used as much, but occasionally the table was pulled out so that people sat around it.  Also, there was more extensive crackling near the window, where there was reportedly some moisture problems at one time.   The rear left side is the side closest to the kitchen, where one imagines children with oily hands may touch the edges, or items are laid for parties.  The center is relatively free from buildup of deep impurities.

Table sanded: Impurity areas consistent

It takes many 1-lb coats, 2-3 per day with several days to cure between, to buildup a base that does not bubble.  After many coats are applied, unevenness is resolved through the final polish.

shellac bar


I am extremely careful about what I wear into the shellac studio.  I put my hair back in a twist, and change into clean tee’s or shirts free of fuzz and that have not been around our cats.  I vacuum and dust the space the day before shellacking.  Still, tiny pieces of fuzz or hairs can come in through the vents in our building, which we share with a props studio for the theatre, and sometimes they land in my wet shellac.  At least a half-dozen of these land in a days’ worth of shellac.  I must remove these so they do not become embedded deep in the finish coat.

Sanding hair

Sanding Hair

Sanded Hair

While the ghost may be seen until the next topcoat, the hair or fuzz itself must be completely removed.  It takes practice to see the difference in the “ghost” versus the hair or fuzz still embedded; you may see pieces of the hair as it is removed float on the tabletop.

Sanded Hair

What saves me is thinking about the studios two centuries ago, with no vacuums, and no Swiffers®  to run over their worksurfaces. (By the way, never use Swiffers® ON the pieces — but they work great all AROUND the pieces.)  Clean early in the day, or even the night before, and allow the room to settle.   In a large studio you can lightly mist the floor if dust continues to plague you, but make sure that the room does not become too damp or that you hit the surfaces to be varnished with the mist.

And what about when you leave a drag or drop or lip?  This happens to the best of us, especially when there are multiple coats in a day without sanding.  The more coats (I never do more than three in one day), the more likely the very last coat may have one or two of these, especially if it is applied by overhead lighting only, after the sun sets.

Again, sanding is key to removing the drag or drops.

My bad

My bad sanded

I always end my best shellac days with a nod to the gods.

shellac bar


1)   Cleanliness is next to godliness.  Wash your hands and face frequently during the day. Why the face?  Because you touch it and pick up oils.  Clean your room as described the night before.
2)   Clean your brush in lab-grade isopropyl alcohol.  Frequently.  I use two clean jam jars for my cleaner, and one is the dirtier of the two.  I wipe my brush on clean paper towels at the end of a row, and then swish the brush through the jar with the darkest color of alcohol, which is dark or dirty from having shellac accumulate in it.  Then I wipe it throughly, and then swish it a second time in a pristine jar of lab alcohol.  Then it is ready for the next row.  Keep your eye on your brush for buildup and clean whenever you see that happening.
3)   We use large canning jars to mix our shellac, and then transfer it into smaller jars to mix our cut for the day.  Watch the buildup around the edges of the jar, and avoid wiping your ]brush on the edge, as it will buildup and get sticky, and if that sticky hits your brush, it will end up on your table.
4)    When sanding, use a light touch and be patient.  Clean and wipe all traces of the sanding procedure with a clean cloth like a diaper cloth, with little chance of adding fuzz to the top.
5)    Lighting is important.  Position your lights so you can see the clear shellac, and change them during the day.
6)    The room cannot be too hot or too cold.  Store your shellac in a cool room, not in the room where you actually shellac, which is warm.
7)    Don’t wear you street clothes, but have clothes that you only wear for shellacking.  No fuzz, no pet hairs, and none of your hairs should be present.
8)    Use the freshest shellac flakes, and never use store-bought pre-mixed shellac.
9)   Always feed the gods, so they may feed you!

©MPF Conservation.  May be printed for your own use ONLY, not for use on blogs without permission.

About dkatiepowellart

hollywood baby turned beach gurl turned steel&glass city gurl turned cowgurl turned herb gurl turned green city gurl. . . artist writer photographer. . . cat lover but misses our big dogs, gone to heaven. . . buddhist and interested in the study of spiritual traditions. . . foodie, organic, lover of all things mik, partner in conservation business mpfconservation, consummate blogger, making a dream happen, insomniac who is either reading buddhist teachings or not-so-bloody mysteries or autobio journal thangs early in the morning when i can't sleep
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