Hi All, I fumed a small white oak table recently for 36 hours in 55 degree high temps, dropping into the 40s overnight. Great results, nice dark brown.
I fumed its twin yesterday. Same hours but 35 degree high dropping into the 20s. Boards are the same, results are weaker. Is there a time / temp chart or rule of thumb for cold weather fuming? I’m not gonna do this indoors.
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I had the same experience a few years ago. Took me 3 days, similar weather. I built a fuming chamber out of firring strips and plastic sheeting, covered any seams with duct tape. I put a small test piece near the opening so I could quickly open, reach in and check it. Even if you had a rule of thumb, I think the tannin content of oak is not the same everywhere, maybe moisture also plays a role, as well as the exact strength of the ammonia you use. So I didn't see any option other than to periodically check.
I've done a fair bit of fuming, and have found that with all else being equal, temperature makes a big difference. Warmer weather promotes better results. Cold weather requires more time in the fumes. That said, all else is rarely equal.
I try to "stack the deck" in my favor as much as possible. I use concentrated ammonia from a blueprint supply store. I make sure my chambers are as airtight as they can be. When the weather is predicted to go below freezing I fume in my attached garage. It never goes below freezing except on the most bitter cold nights. I can open the overhead doors and air the space out if need be.
Mostly, I try not to rush things. I have a large storage container from Rubbermaid that's like a giant Tupperware. After all my fabrication and smoothing/sanding is done, I'll stack all the parts inside with dowels in between like stickers. The stack is spaced off the floor by about an inch using finishing pyramids. I'll add a cup of ammonia in a small dish or just pour it in the bottom of the container. The lid goes on and it sits for three days. I usually let it fume until it stops getting darker. The process goes faster in the summer.
Thanks guys. Longer soak it is. My first time fuming in the cold. (Blueprint / airtight/ PPE all covered) I have a target color as I need to match the first table.
I recently fumed a white oak dining table and tried something new. The shop is a pretty steady 60 to 70 but I tried heating the ammonia solution on a hot plate. At 70F a 10% ammonia solution has a vapor pressure of .1 atmosphere (1.52 psia). At 100F that doubles to .22 (3.2 psia) and at 180F the ammonia is at 1 atmosphere (14.96 psia) and is boiling out of the solution. I was able to accelerate the fuming process to between 3 and 4 hours instead of days. Note that there was also a considerable amount of moisture in the fuming tent and needed a final sanding with 220 grit sandpaper after fuming. Since fuming penetrates relatively deeply into the wood I didn't see any changes in color from sanding.
Note that in the 40's the vapor pressure of a 10% ammonia solution is just over half of 70F room temperature. So while the reaction in the wood is also slowed at lower temperatures I suspect you had much less ammonia in the fuming tent that you thought.
As usual I'd suggest having samples in the fuming chamber and checking periodically for the color change until you get the finish you want.
Also make sure to use a respirator with the appropriate ammonia cartridges since the ammonia concentration in the fuming tent can be rather large using this method. I use the 3M 6004 for my half mask respirator and always use safety glasses.
Kind of like the results I get in the summer. I put my fuming container in the sun. 80 degree ambient plus direct sun speeds things up a bunch!
Interesting thought on the hotplate. I just put mine back outside with 2 jars of 30% ammonia instead of one and will leave it there until Sunday. As I said, indoor fuming is a non-starter here. The only upgrade to your method I'd suggest is a pair of swim goggles to replace the safety glasses. They suck-seal to your face and eliminate any chance of eye exposure.
Follow up: 5 days of soak in the 30s, then it went up to 50. About a week total and the color is perfect. Thanks to all!
Glad you sorted this our MJ. I did find a technical chart in case you want to take a gander at top of page 3. Roughly, you loose about a third of the ammonia vapor concentration from the temp differences you mention. As such, a rough approximation would be to go at least 1/3rd longer. Vapor isn’t the only consideration. The rate of the chemical reactions change when temp chances. It depends on the activation energy of the reaction. For many reactions, activation energies are similar and a rule of thumb we used to use was that for every 10 degree C decrease in temp, the reaction takes twice as long. Going from 50 to 30 F (roughly 10 C change) would potentially make it take twice as long to achieve the desired effect. As such, I would expect it to take 1/3d to two times longer at 30 degrees vs. 50 degrees.
https://www.tannerind.com/PDF/green-aqua-amm.pdf