An experiment with ammonia-fuming black locust wood

[Robert Marshall]

I recently posted about a couple of black locust bowls that I turned:
https://sawmillcreek.org/showthread....k-locust-bowls

In the discussion that ensued, the subject of ammonia-fuming wood, and specifically black locust, came up. It sounded intriguing, so I thought I would give it a try. I had found a ten-year-old post on this forum which included this photo of a fumed natural edge bowl, in which the darkening of the heartwood is very dramatic.

B Locust Lg..jpg
I researched the process, and it appears to be simple. Put the item (bowl) to be fumed into a plastic tent along with a bowl of ammonia, and leave it for a period of time; the ammonia evaporates, and the vapor interacts with chemicals in the wood to darken the wood. The variables are mainly (1) what sort of ammonia you use, (2) how long you allow the process to continue, and (3) temperature in the tent.

I used "janitorial strength" ammonia, purchased from an Ace Hardware. This is 10% ammonium hydroxide, in water. Most household ammonia is much lower in strength (about 1%), and lab-grade ammonia is about 30%, but it is dangerous to handle. The 10% stuff isn't good for your skin, but if you get it on you it can be easily neutralized with vinegar and washed with lots of water, so not a big deal.
Screenshot 2021-09-30 11.09.09 AM.jpg

I used a large trash-barrel clear plastic bag as the "tent." Clear to allow you to see what's happening inside, without removing the wood from the tent. I had the top from a plastic bin as the base, and a plastic 'milk-crate' box as the frame, shown below. I put this all inside the 'tent' plastic bag, opened up so I had access to the inside of the frame box.
Screenshot 2021-09-30 11.13.52 AM.jpg

I put an aluminum tray to contain the ammonia (of the kind used for small pot-pies), and placed it in the center of the box. Wood blocks to either side of the tray elevated the bowl to be fumed, so it sat directly above the ammonia tray, inside down. Added about a cup of ammonia to the tray, then folded the 'tent' around everything, to contain the vapors, and left it in the sun on a deck, for 3 days (and nights). It was sunny and warm (75-80 degrees) during the day, cool at night. The inside of the tent was wet with condensed vapors, and the tray was about half full (vs. being nearly full, when I started). So, the enclosure was full of ammonia vapor. Powerful smell, too, when opened up at the end of the 3 days.

This is the bowl, before fuming (photo is inside, under fluorescent light):

Screenshot 2021-09-30 11.19.38 AM.jpg

This is the bowl, after fuming (photo is outside, indirect sunlight):

Screenshot 2021-09-30 11.25.01 AM.jpg

It is definitely darker, but there is a slight greenish cast to it, also.

All in all, a lot of work to end up with a less-pleasing appearance, in my judgment.

I did a lot of internet research, too. One of the academic studies I looked at said that black locust was the wood most responsive to ammonia fuming, although oak, especially white oak, is the most frequently-used species for fumed furniture (like Stickley Mission-style furniture). Yet my black locust wood did not react dramatically to the fuming.

Questions remaining: (1) Is the 10% ammonia adequate? (2) Does it matter that the item being turned was a "turned-green" bowl, still not fully dry?

Robert

[David Bolson]

Interested, and following, thanks.

I also think it would be important to know what the differences would be after applying an oil finish, which would also darken the wood and bring out the grain.

[Jeffrey J Smith]

A while back (image metadata says 20013) I fumed some freshly turned, very green Black Locust. This was a test piece, fresh from the fuming bucket (5 gal bucket with lid, household ammonia in plastic sour cream container) if I remember correctly, about 4 hours. There's no finish on this just raw turned bowl. This timber started as typically light tan wood. I still have a small piece unfumed.The color is a deep black that has underlying green tint.

This is the only image I've got from this, and no finished, fumed pieces are still in my possession from then. Evidently I didn't document before the survivors left...still have a couple unfumed from the same timber.
9A69600F-B3A4-49D4-8C60-7B07019E2AB1.jpg

[Rob Luter]

I recently posted about a couple of black locust bowls that I turned:
https://sawmillcreek.org/showthread....k-locust-bowls

In the discussion that ensued, the subject of ammonia-fuming wood, and specifically black locust, came up. It sounded intriguing, so I thought I would give it a try. I had found a ten-year-old post on this forum which included this photo of a fumed natural edge bowl, in which the darkening of the heartwood is very dramatic.

B Locust Lg..jpg
I researched the process, and it appears to be simple. Put the item (bowl) to be fumed into a plastic tent along with a bowl of ammonia, and leave it for a period of time; the ammonia evaporates, and the vapor interacts with chemicals in the wood to darken the wood. The variables are mainly (1) what sort of ammonia you use, (2) how long you allow the process to continue, and (3) temperature in the tent.

I used "janitorial strength" ammonia, purchased from an Ace Hardware. This is 10% ammonium hydroxide, in water. Most household ammonia is much lower in strength (about 1%), and lab-grade ammonia is about 30%, but it is dangerous to handle. The 10% stuff isn't good for your skin, but if you get it on you it can be easily neutralized with vinegar and washed with lots of water, so not a big deal.
Screenshot 2021-09-30 11.09.09 AM.jpg

I used a large trash-barrel clear plastic bag as the "tent." Clear to allow you to see what's happening inside, without removing the wood from the tent. I had the top from a plastic bin as the base, and a plastic 'milk-crate' box as the frame, shown below. I put this all inside the 'tent' plastic bag, opened up so I had access to the inside of the frame box.
Screenshot 2021-09-30 11.13.52 AM.jpg

I put an aluminum tray to contain the ammonia (of the kind used for small pot-pies), and placed it in the center of the box. Wood blocks to either side of the tray elevated the bowl to be fumed, so it sat directly above the ammonia tray, inside down. Added about a cup of ammonia to the tray, then folded the 'tent' around everything, to contain the vapors, and left it in the sun on a deck, for 3 days (and nights). It was sunny and warm (75-80 degrees) during the day, cool at night. The inside of the tent was wet with condensed vapors, and the tray was about half full (vs. being nearly full, when I started). So, the enclosure was full of ammonia vapor. Powerful smell, too, when opened up at the end of the 3 days.

This is the bowl, before fuming (photo is inside, under fluorescent light):

Screenshot 2021-09-30 11.19.38 AM.jpg

This is the bowl, after fuming (photo is outside, indirect sunlight):

Screenshot 2021-09-30 11.25.01 AM.jpg

It is definitely darker, but there is a slight greenish cast to it, also.

All in all, a lot of work to end up with a less-pleasing appearance, in my judgment.

I did a lot of internet research, too. One of the academic studies I looked at said that black locust was the wood most responsive to ammonia fuming, although oak, especially white oak, is the most frequently-used species for fumed furniture (like Stickley Mission-style furniture). Yet my black locust wood did not react dramatically to the fuming.

Questions remaining: (1) Is the 10% ammonia adequate? (2) Does it matter that the item being turned was a "turned-green" bowl, still not fully dry?

Robert

The greening coloration is a function of the tannins in the wood. Some oak is known to do that as well. It will darken a bit over time, and especially if a penetrating finish is applied. One of the magical things about fuming is that the wood decides what it's going to do. That is to say the tannin content will drive the darkening, and this can vary throughout the wood. Here's a little Japanese style toolbox I made out of some oak I had. The finish is ammonia fuming followed by danish oil, shellac, and wax. You can see how the intensity of the darkening varied. I got lucky that there was a "tannin free zone" in the center of the planks that wound up looking like a design element. It wraps all the way around.

Your 10% ammonia is fine. Higher concentrations just work faster. The amount of darkening is a function of the tannin content and the time exposed to a given concentration of fumes. I left this in the fumes for about 36 hours if I recall.

[Dave Bunge]

"Questions remaining: (1) Is the 10% ammonia adequate? (2) Does it matter that the item being turned was a "turned-green" bowl, still not fully dry?"

I can't speak for locust, but can give my experience based on fuming white oak.

1. 10% ammonia is plenty strong. I had very dramatic results with white oak using the same, Janitorial Grade ammonia from Ace Hardware.
2. Fully dry might be important. My bowls were fully dry. Certainly the folks making Stickley furniture were treating dry wood. I can see how wet wood, especially if it's above the fiber saturation point, might not change color as well. Ammonia has a high affinity for water. The ammonia vapors from your aluminum pan would dissolve in the free water in the wood. So the ammonia that contacted the tannins in your bowl would be in the water phase. With dry wood, there is no free water for the ammonia vapors to dissolve in, so ammonia vapors would contact the tannins. Perhaps ammonia vapor is more effective at changing the color than aqueous ammonia.

Anyway, I think it's a reasonable hypothesis that wet wood doesn't fume as well as dry wood. Suggest you take the next step in the scientific method and test it by fuming a dry bowl.