Interesting Woodworking Link

Tuesday, September 2, 2008

Episode #71 - Shellac . . . Can You Make The Cut?

Supplies for mixing shellac sitting on my bench

I use shellac quite a bit in my shop. It is a very easy to use finish with a long illustrious history. I try to keep Zinsser spray shellac stocked as a standard shop staple because it is so useful for everything from art projects to woodworking. I also mix my own small batches of fresh shellac from dry flakes for finishing furniture. Keep an eye out for a future episode with a video clip of mixing fresh shellac from flakes and reducing a standard cut to a thinner cut. If you have never used shellac, read on and give it a try . . . you won't regret it!

Shellac a Brief History

Shellac is a natural organic resin that comes from the insect Laccifera lacca indigenous to India and Thailand. During its reproductive cycle, the female secretes an amber-colored resinous substance called "lac” forming a cocoon around the insect and her eggs. The abandoned cocoon, called “sticklac” because it contains resin, twig parts and insect remains, is scraped off the tree by hand, washed and refined to produce the raw material for shellac.

The first commercial use of lac-resin was in the dye industry. About the time that lac-derived dyes were fading in popularity, commercial plants began processing lac-resin for commercial use as a wood sealer and finish. William Zinsser founded the most notable of these processing plants in 1849, Zinsser & Company. Zinsser's shellacs, soluble in denatured ethyl alcohol, were the first quick-drying, tough, bleached or colorless shellacs. Shellac remained the most widely used protective finish for wood until the 1930's when it was replaced by nitrocellulose lacquer. Today, Zinsser is the only company in the United States selling pre-mixed shellac with and without wax.

How to Mix Your Own Shellac


Mixing your own shellac fresh from flakes is not difficult. In fact, the best approach is to mix it fresh as needed. Shellac is mixed according to a specific "cut", referring to the amount of shellac by weight that is mixed in a gallon of alcohol. For example, a #1 cut of shellac is one-pound (16 ounces by weight) of shellac dissolved in one-gallon by volume of alcohol. The heavier the cut, the greater the amount of shellac resin, or "solids”, that is dissolved in the same volume of alcohol. Once mixed, shellac begins to degrade. A useful rule of thumb specifies a 6-month shelf life for freshly mixed shellac, after that shellac no longer dries properly. With this in mind, it is important to mix no more fresh shellac than needed. Conversely, dry shellac flakes have an almost indefinite shelf life if kept cool and dry.

Shellac can be mixed in smaller quantities for use in smaller shops. Take an appropriate sized clean glass jar or plastic bottle with a tight fitting lid. Using the table below, pour shellac flakes and alcohol into the bottle. Close the lid tightly and give it a few shakes from time to time. The shellac will dissolve in a few hours. You can speed up the process by pulverizing the shellac flakes in a small coffee or spice grinder. Once the shellac is dissolved, pour the solution through a clean coffee filter or paint sieve to remove any impurities. Finally, label your container with the pound cut of shellac and date mixed. Now you are ready to apply your own custom-mixed fresh shellac!

I like to use a Braun Coffee Grinder and a small postage scale for mixing shellac. Don’t spend a lot of money for this equipment. I got my coffee grinder for $4 at the local Habitat for Humanity Re-Store!

Shellac Formulas


Shellac formulae can be divided into two broad categories. The first category pertains to mixing fresh dry shellac flakes. The second category is for reducing a premixed cut to a thinner cut.

NOTE: The charts below are available for download.

Category I – Mixing Fresh Shellac From Dry Shellac Flakes

For a standard 2# cut mix 2 oz shellac flakes per cup of alcohol.

Category II – Reducing a Pre-Mixed Cut to a Thinner Cut


To reduce pre-mixed shellac to a more dilute or thinner cut, add the appropriate volume of denatured alcohol to the appropriate volume of shellac per the chart below. For example to get a 1/2# cut from a pre-mixed 2# cut simply a 2 parts of denatured alcohol to 1 part 2# cut shellac. I like to use a large volume syringe obtainable from a vet or feed supply store to easily draw up volumes of alcohol or shellac. The syringe is easy to disassemble and clean with clean alcohol. Use one syringe for shellac and one for alcohol to prevent contamination.


Liquid Measure Reference
  • 16 ounces = 1 Pint
  • 32 ounces = 1 Quart
  • 64 ounces = 1/2 Gallon
  • 128 ounces = 1 Gallon
  • 2 Pints = 1 Quart
  • 4 Quarts = 1 Gallon
  • 1 Cup = 8 Ounces
Interesting Alcohol Facts
  • Ethanol is the same alcohol found in alcoholic beverages
  • Denatured alcohol has been altered with additives (i.e. methanol) rendering it unfit for safe human consumption
  • Proof refers to the volume of pure ethanol as a percentage divided by 2
  • 200-proof ethanol means 100% ethanol
  • 190-proof ethanol means 95% ethanol
Some Interesting Shellac Facts
  • Shellac is easy to apply with rag, brush, paper towel, sponge, or spray gun
  • Shellac adds a subtle bit of color to wood popping the grain
  • Shellac won't yellow much with age compared to varnish and lacquer
  • Shellac is the perfect barrier coat between incompatible finishes
  • Shellac prevents pine pitch from bleeding
  • Shellac dries fast making runs & sags less likely
  • Shellac is perfect for restoration since it is easy to sand, repair and remove
  • Shellac dries hard
  • Shellac is easily repairable since the new finish melts into previous layers
  • Shellac can be tinted ( LockwoodTransTintMixol )
  • Shellac dries quickly allowing you to recoat with thin coats in less than two hours
  • Shellac finish errors are easy to fix by leveling your finish with a scraper or razor
  • Shellac is a non-toxic finish when dry
  • Thinner cuts of shellac are easier to apply and dry faster
  • Shellac is a USP-approved food & medicinal coating
  • Shellac “spit coat” is a 1/2# cut of dewaxed shellac used as a barrier coat between stains & finishes
  • Zinsser’s Seal Coat Universal Sealer is a 2# cut ready-to-use dewaxed shellac
  • Zinsser Bulls-Eye Clear & Amber Shellacs are both 3# cuts
  • Zinsser Clear & Amber Bulls-Eye Shellacs contain natural shellac wax
Useful Shellac Links

6 comments:

doug said...

Nice little lesson there on shellac. Just the right amount of information for a quick work break. I will be interested in your follow up. Have you tried dyes with your shellac?

David Pruett said...

Doug -

Thanks fro stopping by and leaving a comment. I have really enjoyed working with shellac and thought I would share a summary of what I've learned.

I have experimented with dyes but not mixed with shellac. I do plan on playing with this so look for an updated post in the future.

David

Vic Hubbard said...

David,

I'm always amazed at your posts. You really are a born educator. I think I see shellac in my future.
I'm must be a born prognosticator!

David Pruett said...

Vic -

Always good to get a comment from you and The Tumblewood Blog! Well my friend, I have to politely disagree with you being a prograstinator, especially after seeing the series you posted on Noah's Toy Crane. That was an absolute masterpiece!

I appreciate your kind words. Trust me, after you play around a bit with shellac you will reach for it often!

David

Shannon said...

Dave,

I saw this come up in my email subscription and made a note to read it when I had the time to concentrate on it because your posts are always jam packe. You did not disappoint this time either. I love shellac and this post makes a great companion to Flexner's new post in the latest Pop Wood mag. Great work thank for sharing your knowledge.

David Pruett said...

Shannon -

Thanks! I greatly appreciate the feedback. I do have a short shellac video in the works.

David