Boiling Protocol Tips and Tricks

Boiling Protocol Overview: For the last several years, I have conducted extensive tests of my protocol and various other methods to dry green timber. The purpose of my research and testing is to develop/refine various methods to dry green wood as quickly as possible, with the absolute minimum amount of defects. Since my original boiling protocol on reducing drying degrade was published several years ago, I have continued to perfect and hone this protocol.

Continuous improvement of all of my studio’s protocols is a high priority; therefore, I am never content to rest on previous successes. I have received hundreds and hundreds of emails and numerous phone calls regarding my boiling protocol for reducing drying degrade in green timbers. In addition, in my weekly demonstrations around the United States, I have met thousands of woodturners who have tried my boiling protocol with great success.

However, I have found that some woodturners who tried my boiling protocol have not achieved the same high level of success. Some of these turners have called or emailed stating they were having spotty results with boiling, or have not achieved an acceptable level of success. In each of these instances, the turner has allowed errors to be introduced into the protocol, which has resulted in lower success ratios.

In an effort to assist those who are interested in the boiling protocol, I have complied the following list of boiling tips to help you with implementing the boiling protocol successfully in your studio. The boiling protocol has allowed me to dry a tremendous amount of bowls, platters and hollow forms with no cracking whatsoever and it is an integral part of my studio’s drying protocol. Here is a recap of the boiling protocol for those who are unfamiliar with my original article on boiling wood to reduce drying degrade. (Published in my first electronic book - "Woodturning with Steven D. Russell, Volume I."

Green wood bowls ready for boiling

Getting Started with the Boiling Protocol

A standard 55-gallon drum cut down to 18" high is used for boiling.

I prefer to use a 55-gallon drum for the boiling pot. This has been cut down to 18" high. The pot is heated with a Cajun-style propane burner, which is typically sold to fry turkeys or boil seafood outside. If you live in a rural area, you can easily heat your pot with scraps from your studio. Whatever container you decide to boil in, use a pot that you can dedicate exclusively to timber boiling. The extractives in the timber will quickly make a mess of your boiling pot and you will not want to use it for anything else.

In the past, I boiled my rough outs with a full rolling boil for the entire boil cycle. I found out that this was not necessary and just wasted propane. Now, I bring the pot up to a boil and place the bowls and platters into the "soup." You need to produce an active medium boil, not a simmer. A full rolling boil can also be used, but it does not generate any increased success.

You must monitor the pot to insure it does not boil dry. Periodically, you will have to replace some of the water lost during the boil. I replenish the water in between boil cycles to prevent any compromise of the boiling cycle. You can also cover the pot with a lid to help retain heat, water and conserve fuel. The boiling water may slosh out and stain some surfaces, so take precautions to insure that you have suitable protection.

All pieces in the boiling pot must be submerged during the boiling process. A simple grate can be made of concrete rebar scrap that is wired together and will fit inside the boiling pot. A weight is then added to insure that the grate keeps all pieces submerged during the boiling process. If you do not use the wire grate, you can use a weight to prevent the pieces from floating. A brick or a large rock works great for this. Sometimes, the design will limit the amount of pieces you can put in the boiling pot, semi-enclosed bowls, hollow forms, such as tall roughed out vases, etc. However, I load as many pieces as I can fit in the pot. You can load quite a few platters into the pot, because they stack so well.

A Cajun-style propane burner is used to fire the pot.

CAUTION: Do not load pieces into the boiling pot that are near the same size as the maximum diameter of the pot. When the wood takes up water during the boil, it will expand in size. If the piece is near the same size as the pot’s diameter when you place it in the pot to boil, the wood will swell, creating a tight fit, or plug in the pot, causing a build-up of pressure under the plug.

This is a dangerous condition that can cause severe injuries. For safety, always allow 6" of free space around your boiled pieces in the pot as a safety margin. For example, if your pot measures 24" in diameter, the maximum size piece you should ever boil is 18". If you need to boil larger pieces, get a larger pot, observing the 6" safety margin.

Boiling Protocol: Tips for Success

• My basic boiling protocol requires 1 hour (60 minutes) of boiling for every 1" of wall thickness. This means you must measure the wall thickness of your pieces to insure you are boiling for the correct time. Ignore any tennon/spigot thickness less than 3/4" and measure the belly, or wall of any bowls, or platters.
• If a batch of bowls/platters includes mixed thickness walls, you must set your boil cycle for the thickest piece in the pot. For example: If you pot contains 1.0", 1.25" 1.5" and 2.0" thick walled pieces, you must set your boil cycle for the 2.0" thick wall (i.e., the mixed pot would boil for 2 hours total).
• Boiling longer than the protocol requires will not compromise the boiling protocol, but it will not help either. However, boiling less than the required time will result in a success rate well below the established and documented 95% or better of boiled pieces dried with no checking.

When placing bowls into the boiling water, you must wait until the water returns to a boil before starting your timing cycle. This is critical to obtaining a proper boil cycle. Placing cold bowls into boiling water stops the boiling process. If you start your time cycle before the water returns to a boil, you will not be getting the required 60 minutes of active boil per inch of wall thickness that is required for best results.

Loading bowls into the boiling pot.

• If the pieces float during the boiling cycle, your success ratio will be lower. To prevent this you can fashion a metal grate to fit inside the pot, which is slightly smaller than the diameter of your boiling pot. By placing a sufficient weight on this grate, all pieces in the pot will be prevented from floating during the boiling cycle.
• Whilst rough turning a batch of bowls for the boiling pot, insure that any previously turned bowls do not sit in the open air prior to boiling. I use a plastic tarp to cover the pieces, or place them into a plastic trashcan with a tight fitting lid. Boiling will not glue any pre-existing cracks back together.

Unloading bowls from the boiling pot.

When you remove your bowls from the boiling water, you must protect the bowls from rapid drying of the surface fibers. My preferred method is to place the boiled pieces onto the floor in a cone or pyramid shape, alternating the rims and tennons. Cover the pile with a canvass tarp or old bath towels. The boiled bowls cannot be left in the open air, or they will develop cracks. They cannot be covered with anything that does not allow the water vapour to escape (plastic for example).

• To remove some of the excess water from the bowls, leave the bowls under the fabric tarp for two to three days. Invert the pile once each day (rims up, rims down, rims up etc.) for three days. At the conclusion of the three-day period, place the bowls into paper grocery bags and seal the open end of the bag with tape or staples. Leave the bowls in the bag until they reach equilibrium moisture content. Paper bagging is the best environment to dry the post-boiled pieces in for most people.

The paper bag creates a microclimate inside the bag of higher moisture content than the outside ambient atmosphere. As the water vapour moves out of the bowl, it is impeded from quick dissipation into the ambient atmosphere because it must first pass through the craft paper bag barrier wall. In addition, the bag prevents any drafts from drying the exterior of the piece too quickly, preventing steep moisture gradients from forming.

Placing a boiled bowl in a paper bag for drying.

• The bowls can also be waxed and then dried in the open air, but I prefer to place them into paper bags. It takes less time and keeps the cost of using the wax emulsion (cold wax emulsions are typically paraffin, or microcrystalline based, with the wax, water and a surfactant) down. Tyvek bags can be used in lieu of the paper bags. Tyvek is a specialty film developed by Dupont that allows moisture vapour transmission in one direction only and is used extensively as a house wrap before adding brick or siding.
• With highly unstable timbers like green Madrone Burr, put the items into cool water and then bring it up to a boil SLOWLY, over the course of two hours. When the water begins boiling (2 hours from the start), boil for two to three hours. When this cycle is up, (4-5 hours from the start) turn off the burner and let the piece sit in the pot until the next day. Then, remove the items from the water and air-dry them for a couple of days before bagging. However, most timbers do not require this extra effort.

Additional Benefits of Using the Boiling Protocol

• On average, boiling will reduce checking in boiled pieces to 1.5% to 4.0% or less per hundred, depending on the species. This success rate is not only from my studio’s efforts, but has also been achieved by hundreds and hundreds of turners around the world with their local species.
• Boiling will decrease drying time on average up to 50%. For example, if a non-boiled piece takes 6 months to air dry, a boiled piece of the same timber will typically reach EMC (equilibrium moisture content) in three months, or less. Some timbers will see reductions in drying time of up to 83.5%. EMC is defined as the point at which the moisture content in the timber is at equilibrium with the ambient atmosphere.
• Boiling will reduce warpage on average 5%. Although this is not significant, the protocol does produce an average reduction in overall warpage of 5%.
• Unwanted guests in the bowls, i.e. worms, bugs and other critters are usually taken care of during the boiling cycle.
• I am frequently asked about colour loss in boiled pieces… Having boiled thousands of pieces from more than 46 different species, I can well attest to the fact that I see no difference in core colour loss in boiled pieces. There is in fact some leaching of the surface colour (about 1/16" of an inch), but below that, the colour is normal. Remember we are boiling roughouts, so the trivial loss on the surface is irrelevant, as it will be turned away when the piece is trued up for finish turning.

Boiling Protocol Contraindications

Through the years, my boiling protocol has been the best and most successful drying protocol I have ever used in my studio. However, as good as boiling is, it is not 100% perfect and it is not necessary for all timbers. Whether you experiment with boiling or not is up to you. If you are satisfied with the drying success rate of your current drying protocols, then I see no need to change. If however, you are getting lots of cracks on your bowls during drying, or you want the roughouts to dry faster, then give boiling a try.

Stable timbers do not require boiling, unless you want to speed the drying of the roughout. Local timbers in my area that I rarely boil include White Ash and Honey Mesquite. Both of these timbers are so bullet proof that boiling is unnecessary. There are no doubt timbers in your area that are also very stable, and you will not need to boil them to reduce drying degrade. This boiling protocol is never going to be 100% perfect, with 100% of the timbers, 100% of the time. I have never found any drying protocol that is 100% perfect, 100% of the time. Sometimes, Mother Nature will win the drying game. However, when used properly, the boiling protocol can be a valuable tool in your studio, saving you time, money and valuable wood.

After the boiled bowls have reached EMC, they can be nested on shelves until needed.

Safety Note: Always follow all manufacturers safety instructions before working with your lathe, or any of the tools or products you may use. If you are unsure about any operation, obtain competent professional instruction before proceeding. Use and wear all necessary safety devices during turning and observe safe woodturning practices to prevent accident or injury.

Steven D. Russell is a professional studio woodturner, teacher and writer. He has written numerous articles for international woodturning magazines, which have been published in more than 78 countries around the world. Steve has demonstrated in numerous cities across the United States. His studio, Eurowood Werks, specializes in bowls, platters and hollow forms with unique visual and tactile treatments.

Steve is also a regular featured writer for the Guild of Master Craftsman's "Woodturning" magazine, published in London England. Woodturning magazine is the world's leading magazine for woodturners. Look for his monthly articles covering technical topics, or project based articles in each issue.

If you have any questions about Steve's boiling protocol or would like to share your experience using his boiling protocol, please feel free to email him at Woodturning Videos Plus