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Shellac Shelf Life -The Followup  

10/20/2011

When we last spoke of shellac our hero had said all my shellac dissolves send me some dewaxed shellac and I will try to dissolve it. We had found that just about everything dissolved if we agitated it enough. Large chunks weren't a problem either - agitate and all was well. even better than lots of old flakes. We found that most people didn't agitate enough.

Live and learn.
Two challengers picked up the gauntlet and sent us samples. Patrick Edwards send us a bag of 8 or 10 year old platin ( a highly refined blond) and Mark Schofield of Fine Woodworking sent something I think about 3-5 years old.

Mark's stuff sort of dissolved - it needed a lot of agitation but there was residue - ghost flakes that would not go away, I would not call it dissolved. Patrick's stuff just laughed at me. But now we had real samples that did not dissolve.

The problem was figuring out how to get shellac to not dissolve quickly - we didn't need an answer in three years. It took some doing but it turned out destroying shellac is pretty easy to do. Oxygen! if you take some perfectly fresh shellac, put it in a bag, fill the bag with oxygen it will quickly lose it's ability to dissolve.

It's not heat, it's not humidity, it's oxygen.

Waxed shellac has a very very long shelf life because the wax protects the shellac. The coating of wax keeps the shellac from clumping in the heat and it prevents the oxygen from getting to the shellac. Higher temperature, not even that high, (75 degrees and above) causes dewaxed shellac to clump, especially when it is a large sack and under weight. This is annoying but the clump does limit the contact oxygen has with the insides of the clump. The biggest problem comes about when shellac is repacked into regular plastic bags and jars. These containers are all permeable to oxygen so over time - several years the outer layer of shellac flakes oxidizes (or the oxygen speeds up a polymerization process I don't know but the result is the same) and the shellac won't dissolve. For the first several years the oxidation layer is thin so agitation solves the problem - the actual amount of skin that won't dissolve will be minute and unnoticed. But after a few years the entire flake won't dissolve. Chunks as I said, have a longer shelf life.
If you put the shellac in a refrigerator the low temperature will slow down the reaction and refrigerators are also air tight so there is a limited amount of oxygen to for the flakes to oxidize with. The low temperature also keeps the shellac from sticking together which isn't the same as stopping oxidation but people hate breaking up chunks and associate (erroneously) the chunks with aging.

The solution to the problem.

All our shellac, both the Tiger Flakes and BT&C shellac that we sell through Woodcraft, now come in resealable oxygen barrier bags, and include an oxygen absorber. We store all our stock in a refrigerator, and we do not ship shellac wholesale during the summer (and haven't for several years). All the new batches of shellac are labeled so that we can trace back anything bad to which shipment it was. We also test every bulk bag of shellac we import to make sure it dissolves properly when we get it. The photo above is a box of sample dissolve tests from our last packaging run. We are not sure if refrigerator storage is necessary except to prevent clumping as the cold will also slow the oxygen absorption. We are testing that now.

Our goal is mostly to ensure that the shellac that we, Woodcraft, and the Woodcraft stores warehouse will be fine when you buy it. The flakes might be clumped if it got exposed to heat - not everyone refrigerates - but it should dissolve fine. Of course when you get the shellac, you should reseal the bag once it is open, and store the flakes in a cool place.

As far as we know we are the first vendors to pack shellac in a way that will extend its shelf life and while we are continuing our tests we are very optimistic that this will help everyone have fewer problems with their shellac. Incidentally we don't actually have many reports of problems. It's only an issue for shellac that has been sitting for a bunch of years.

A question people do ask is why don't we just sell waxed shellac? For two reasons, one we think the finish you get with dewaxed shellac is cleaner and harder. The second reason is that while most people know to just let the wax settle it's an extra step that beginners may neglect and end up having problems.

In other news:
On the alcohol front: after months on being out of stock we finally have available BT&C 200 Proof Ethanol. This is the best stuff for dissolving shellac that we know of. The problem was that in order to sell denatured alcohol this pure we needed a special permit. We now have it. The only fly in the ointment is that I don't know if when we run out of our current stock if we will be able to get more.

On the shellac front: for the past few years the shellac crop in India has failed. Shellac prices have soared! Since we don't want to warehouse shellac just to protect ourselves against price rises - we actually fly the stuff in for freshness - you will see another price rise, if not by the end of the year, shortly after it.


Tags:Woodworking Tools and Techniques
Comments: 9
10/25/2011Luke Townsley http://UnpluggedShop.com
Joel,

Interesting stuff. I do have a question about the alcohol. I've never really used shellac, but am thinking about it for my woodturning and some other stuff.

Regarding the denaturing of the ethanol, is it "food safe" if the denaturing is put in to make it inedible? If I want 100% food safe, should I just go to the store and get the strongest vodka I can find?

Thanks,
Luke Townsley
10/25/2011joel http://www.toolsforworkingwood.com
Denatured Alcohol is any alcohol that is made undrinkable, usually by the addition of the very poisonous Methanol. Our stuff is less poisonous which is why we needed a permit to sell it.
If you want to use something drinkable. Very high proof vodka will work. EverClear - which comes in two proofs - get the higher proof. Our stuff also has little or no water - so it will work better than Everclear but EverClear is the next best thing
10/27/2011Doug Berch http://dougberch.com
I read somewhere (I think it was a very old issue Popular Mechanics) that you can put some uncooked rice into a bottle of alcohol to absorb and separate any water that gets into it. I haven't tried it myself but it seems like an interesting idea.
10/27/2011Chuck Beck 
Joel,
I seldom use anything but shellac for finishing, but I recently found a jar of shellac flake that I had hidden from myself that I jarred in Aug '07. It was in a cleaned glass jelly jar in my basement shop in a dark corner. I dissolved it 2 nights ago to about a 2lb cut and tonight is was completely dissolved. It dried to the touch in about 15 min after further thinning and HVLP spraying.
So, how do you feel about sealed glass storage?
10/27/2011joel http://www.toolsforworkingwood.com
If the seal in the glass jar is good - then you have an airtight container and the shellac will last - depending on how full the jar is. Without a good seal you are back to square one.
10/29/2011Adrian 
I have a bag of shellac that is probably six or seven years old and have never had problems with it dissolving until recently. I got a couple flakes that wouldn't dissolve.

Does this mean I need to throw it away and get new stuff? Or should I strain out undissolved flakes?
10/29/2011Charlie 
Wow - THANKS! Been wondering about the conclusion of the challenge. I appreciate the explanation. Now I have a shot at better preservation of my flakes.
10/29/2011joel http://www.toolsforworkingwood.com
Strain the flakes it should be fine. Since you should be testing your finishes anyway - a quick test with what remains should tell you if all is OK. The only issue is that your final cut is the shellac that gets dissolved so make sure what you end up with is strong enough or use less alcohol.
11/07/2011David Keller 
Joel - Regarding what happens to shellac as it ages: Shellac is, in chemistry-speak, an ester. Esters are compounds that "hydrolyzable". That is, the ester bond can be severed by reacting with the hydroxyl radical (the paper representation of this chemical entity is -OH). The severed components of shellac after it is hydrolyzed are largely insoluble in ethanol, hence the dissolution problem.

It is also possible to oxidize the ester bond, so you are correct that exposure to oxygen will cause the shellac to degrade.

But the potential is there to degrade shellac in the absence of oxygen, so long as water vapor is present. These degredation reaction, like all chemical reactions, is affected by temperature. Roughly speaking, any chemical reaction's rate will double with a 5 degree Celsius rise in temperature. This explains why storage in a hot, humid warehouse will rapidly degrade shellac over time.

From the standpoint of storage for a home woodworker, the best & easiest solution is to use a non oxygen permeable and non water vapor transmissible container. The most common is a Mason jar - glass has no appreciable permeability for either oxygen or water vapor. Storage of this container in the refrigerator (or even the freezer) will further slow down the degredation. A caution is relevant here, however - if you store shellac in cold conditions, and are impatient and open the container before all of the contents have come to ambient temperature, water vapor from the surrounding atmosphere will condense on the contents, and that water will ruin the shellac over a fairly short period. It takes quite a bit of time for a pound of shellac flakes to come to temperature when enclosed in a sealed mason jar - perhaps an hour or so at 75 deg F.

Finally, you can "roll your own" oxygen scavenger and dessicant (water absorber) for your mason jar if you so choose. The brand of pocket warmers called "hot hands" works by absorbing oxygen from the air to oxidize iron filings, the by product of which is heat. In an enclosed, oxygen-impermeable container, the rise in temperature will be very minor, as all of the available oxygen will be consumed very quickly. To make a moisture-adsorbing dessicant, spread dry rice onto a cookie sheet in a thin (1/4") layer. Turn the oven on to about 250 deg F, and place the rice into into it. Allow the rice to bake for about 45 minutes, opening the oven door relatively frequently to allow the water driven off of the rice to escape. After baking, rapidly pour the still-hot rice into a moisture-impermeable container and seal it. Metal cookie tins work well for this purpose, as do mason jars. Allow the rice to come to room temperature (generally several hours). The rice will then act as a very efficient moisture-adsorbing dessicant so long as it is stored in a moisture-impermeable container.
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