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JOEL Joel's Blog

Alcohol - Ethanol, Methanol, Isopropyl , Water, and French Polishing


Alcohol - Ethanol, Methanol, Isopropyl , Water, and French Polishing 4It's a bright sunny day in late spring with not a trace of a breeze. On the lake the rays of sunshine pierce the water and illuminate the lake bottom. The water is clearer than glass and you can see every pebble, every plant and every bit of sand. The water makes everything feel clearer and have more depth. A pebble on the shore is just a gray pebble but on the water bottom the pebble seems shinier, the color has more depth. The lake bottom is alive, bright. Then along comes a small fish swimming by.

Properly done a French polish gives the same effect of depth and brightness - just without the fish. Glass is a poor cousin to a good French polish. The wood has depth, and a gloss that looks perpetually wet even though it is hard and dry.

And if you pay attention to what you are doing it's not that hard to do.

In my previous blog entry on shellac I showed how we trivially dissolved fairly old hunks of shellac so that we could do a little French polishing. I did forget to mention that as near as we can tell clumping in the package is caused by heat and doesn't effect dissolving. We took the shellac we dissolved and Ben French polished a scrap of poplar. We did not filter the shellac, although if we were spraying filtering is a good habit to get into.

Here's how Ben did the sample shown above. It was his first time French polishing.

1) wet wood to raise grain and let dry
2) Scrape surface smooth
3) Brush coat of 1lb cut and let dry
4) sand with 320
repeat steps 3-4 until the wood takes the brushed shellac evenly without leaving any quick drying spots.
For this piece of poplar it took 3 coats.

5) let dry over night
6) Sand everything one last time

7) Begin French Polish! using a piece of t-shirt as my pad and 2lb cut and mineral oil from Duane Reade

Here's how: Apply shellac to rag and tap into palm to distribute the shellac, then I dip a finger in mineral oil and spread it on the surface of the pad, and tap it into my palm again.

I didn't stop between coats because the shellac dries as its applied. To tell when to add more shellac to the pad I watch the trail left by the pad as it moves over the surface. The trail is less reflective foggy looking for a very short time. The trail is longer when the pad is more shellacky and shorter when it's less. When it shortens to about 1 or 2 inches I re-up on shellac. When the rag feels grippy I re-up on oil.

8) After it looks good I put lighter fluid on a towel and wiped the oil off.

For the polishing I pretty much followed Flexner's instructions save for his suggestion to increase the ratio of alcohol to shellac at the end of the polish.

The reason the finish has such clarity and depth to it is because the shellac is pure and there are no air or water bubbles trapped in the finish. Also we are giving enough buildup so that the top surface is flat and reflects light.

Now let's discuss the role alcohol plays in all of this.

Alcohol loves water, They mix together and traditionally made alcohol, even a top grade, will have a decent percentage of water in it from the distilling process. Alcohol loves water so much that if you leave alcohol that doesn't have any water in it in an open container it will absorb water from the air. Water molecules on the other hand hate shellac. So if you finish with shellac the water in the alcohol will create microscopic pores that can cloud the finish, give a softer finish, and lengthen drying times. I have a sneaking suspicion about which more testing is needed that one of the reasons for rubbing on all the coats for a fine French polish was to allow the water in the alcohol time to evaporate before it got trapped as it would in a heavier coat of shellac.
In recent years anhydrous alcohol has reached the finishing market. Anhydrous simply means that the water in the alcohol has been removed. It's done by additional refining of the alcohol. Practically what happens? We will find that it's easier to get that mirror sheen and a hard finish. In the "French Polished" example above it wasn't really French polished the way a French person of the last century would do it. We did rub on the finish but we didn't thin out the shellac at the end and we didn't use any rottenstone which polishes the wood and helps fill the pores of the wood. It went pretty quickly but even with the shortcuts what we got was a hard finish, with a deep sheen and depth that is just awesome.

Another reason that this quality of finish was so easy to achieve was because the alcohol we used was 200 proof Ethanol. It's actually 199 proof because it has a rubber solvent denatureant as required by law, but the industry calls it 200 proof. In any case it's Ethanol. Ethanol is an alcohol with a very low flash point, that means it dries fast so as you are rubbing out the layers you are actually rubbing out shellac not just pushing around wet finish. Almost all hardware store alcohols not only contain water, they also contain methanol and isopropal or other alcohols along with it. Aside from the fact that methanol is a lot more dangerous to be around than ethanol these alcohols don't flash off as fast. For spraying a little more time so that the alcohol doesn't dry between the time it leaves the sprayer and hits your work is a good thing - so a little isopropal alcohol in the mix as a retardant is a good idea. But for French polish, and in general brushing and rubbing out shellac our testing indicates that the faster drying times of pure ethanol makes for a harder, shiner finish that goes on easier.

French polishing is a skill that isn't hard to learn. I know you can have successful results with just about any quality of shellac and alcohol but using the best stuff available makes the job go faster, go easier and produces a finish that will make you want to dive into the surface of your work.
Join the conversation
10/19/2010 Paul
I've had a try at French Polishing. The day was hot and the rubber was always sticking and dragging on the wood. As an experiment I dissolved the shellac flakes in isopropanol (propan-2-ol). Isopropanol feels oily and I thought the isopropanol would lubricate the rubber as the shellac was applied. The desired effect did not eventuate and the rubber still stuck. It was worth a try.

I've managed to get hold of some mineral oil and next time I want to try French Polishing I'll follow your method (on a cool day).
10/19/2010 Tico Vogt
Great post, Joel. I've waited forever to try my hand at French Polishing. There always seemed too many potential hassles along the way to really get me inspired. Now it appears that the obstacles have been identified and overcome. It looks like the time is at hand.

Thanks for the research.

10/19/2010 Mark
Please emphatically advise folks to NEVER use methanol- It is a cumulative neurotoxin that is absorbed through the skin fairly rapidly, where it is metabolized to formaldehyde and kills off your nerve endings. Inhaled as fumes, it does the same thing to the brain. Nasty, nasty stuff!
You are 100% right about methanol, unfortunately the regular alcohol sold in hardware store, even if it is mostly ethanol usually contains 5-10% methanol (along with isopropal alcohol and water). Even if the results were the same as with 100% ethanol from a safety standpoint I would not use it. It's one of the reasons I am so happy to be able to offer 100% ethanol in our store. If you are forced to use the stuff make sure you have the correct gloves and face masks.
10/19/2010 Ron Hock
I learned a great tip from Brian Burns, guitar-maker and smart guy: use mineral spirits (paint thinner) instead of mineral oil as a lubricant for the pad. It works just as well and dries off. Saves the step of cleaning the mineral oil. You can apply the mineral spirits quite liberally. Try it!

Good post, Joel.
10/19/2010 Luke Townsley
Great post, Joel. I've never seriously considered working with shellac, but you make me want to try it.
11/12/2010 Mark Gray
I've never heard that about methanol or Wood Alcohol, it came in chemistry sets when I was much younger and maybe that's my problem. But there is always someone out there who is doing it for all " Our own Good."

It is like the French Polish Zinnser tried to sell until the EPA said oh no you can't sell that too much Denatured Alcohol in it. Yet I can buy a couple of gallons of Alcohol at my local hardware store. But you can buy it in Canada. Go figure.

Nice blog Joel. Also great article too.

One question though. I read somewhere on French Polishing where they listed ingredients Benzoin( which I found) and Sandarrach this item no one seems to know what in the world it is. Have you ever heard of it.
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