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JOEL Joel's Blog

BT&C Pumice has Landed

05/06/2020

BT&C Pumice has Landed 1
With all that time on your hands cooped up at home and in the home shop, you might have finished that project you were working on -- except maybe for the final finish. If that's the case, I have the perfect time-waster for you. Did I say time-waster? I mean educational opportunity. True "French polishing" produces not just the finest finishes I have ever seen, it's labor intensive, which means in the time of quarantine it's a really productive good use of time. And it's also good exercise - remember the Karate Kid - Wax On Wax Off (see below) - which is just what you need in these times of enforced sedentary behavior.

We used to get our pumice from Behlen, but the company was acquired and Behlen products were discontinued. Our guy Eddie O'Donnell, who does our great finishing videos, is a luthier who does a lot of French polishing on his instruments and so needed good pumice. Now when it comes to new products we like to go all out. So we tested pumice and what we ended up with is American White Pumice in 2F and 4F grades. I have always hated pumice that came in bags or bottles - it just gets everywhere. So our pumice comes in an easy-to-grasp cardboard tube with a shaker top. It's much easier to use. You don't have to find yet another container to store the stuff in or have a bag spilling out floating abrasive everywhere.

I've always been blown away by French polishing. It's the difference between looking in the murky Hudson River versus staring into a crystal clear pond with still water. The depth of the finish is amazing. It's also conceptually a very simple finish. What you do is take a pad charged with a little shellac and pumice and rub it continuously over a surface. Each pass of the pad, called a "rubber," deposits a ultra-thin layer of shellac on the work, dissolving and adhering to the previous layer, while at the same time the pumice polishes the wood and creates a mixture of pumice and sawdust that the constant rubbing forces into and fills pores in the wood. Pumice is a fairly soft, gentle abrasive which is why it works so well for finishing: it abrades without scratching. As you are depositing a very thin layer, the alcohol in the shellac flashes off instantly and the finish dries. Also, because you are instantly dissolving and re-hardening the previous layer, the rubber's actions - making consistent contact with the surface - you end up with is a pure shellac finish with no microscopic pockets of trapped air. This is what gives the finish its incredible transparency. The filled pores give that mirror surface.

The exact sequence of French polishing depends on how you are trained. Some people do the pumice separately; some don't use it; some brush on a thick layer of shellac and then French polish. There's also a whole vocabulary of words to describe all the stages of the work.

We sell flake shellac, so it makes sense that we try to be a one-stop shop. We liked the obvious advantage of a nice container with a shaker top, but the contents mattered even more. We did a lot of testing to make sure we were selling the right stuff. Our pumice is a top grade white pumice that is mined in the USA. According to Eddie's tests, white pumice plus sawdust filled pores are marginally lighter in color than using regular pumice. The most popular grades of pumice are 2F (medium) and the finer 4F. We did test two even finer grades of pumice, thinking that if 4F gets you a wonderful result, even finer grades would get you double-plus wonderful results. Sadly, this proved to be untrue. Eddie thought the finer grits didn't produce a finer result. So we aren't carrying them.

And before you ask: both flat and curved surfaces can be French polished. Carvings and such get brushed with shellac.
You can find our pumice here and shellac here and here.


Join the conversation
05/06/2020 Paul Bailey
Way back in the 60's ("long before wax on, wax off") a pumice finish was standard in our high school shop class. Mr Battles, our teacher, was a fanatic about a beautiful finish - and I still have the pool cue case I made under his guidance.
05/12/2020 Wade Hutchison
We were taught pumice then rottenstone after "spirit" varnish. I don't make many things that require a polished finish, but it's nice to know the traditional materials are still available. Keep up the good work.
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