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curly cherry finish tests #1: tung oil etc.

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Blog entry by harum posted 08-12-2015 12:07 AM 1407 reads 0 times favorited 5 comments Add to Favorites Watch
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Continued testing finishes for curly cherry started with varnishes and shellacs. Having read much about how tung oil brings out chatoyance, I applied for comparison one coat each: (a) 2 lbs. cut ruby shellac, (b) pure tung oil from Woodcraft, and ( c) Bulls Eye seal coat from Zinsser.

The shellacs gave good chatoyance without much blotching. The oil initially gave quite a depth, chatoyance and color, more than the shellacs. However, some spots became quite dark, so the sample (b) appears blotchy; the depth and chatoyance of the figure later almost disappeared, the color contrast stayed.

Oil application: I rubbed the 1:1 mixture of tung oil and paint thinner into the surface, then rubbed again where it got absorbed into the grain for the next 15 mins., and finally wiped the oil completely off.

I did this about two weeks ago. I kept the board in the garage and every day wiped off whatever new drops of oil wept back onto the surface from the grain. It looked as if the oil would never cure: the surface was always oily. This morning I put the board outside thinking it would speed up the curing process.

By the evening tiny drops of oil again wept back from the grain… But they have hardened and can’t be wiped off! And the entire tung oil sample no longer feels oily.

Two weeks in garage did nothing and one day in the sun/wind did the job?

The cured(?) tung oil sample feels rough, as if the grain was raised, asking for some sanding. Does tung oil need moisture for curing?

Right now the tung oil doesn’t look better than the shellacs. It’s blotchy, of darker color, barely any chatoyance, the grain is raised. It doesn’t even look good enough to be an option as a finish. Considering that some swear by pure tung oil, confusing…

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."



5 comments so far

View ellen35's profile

ellen35

2724 posts in 2895 days


#1 posted 08-12-2015 11:06 AM

Did you try the shellac followed by the tung oil/mineral spirits mix? I did that on a bench and it came out very well. I did wipe on several coats of the mix (to which I added Waterlox original – equal parts of each – and yes, I do know that Waterlox also has tung oil in it) after the shellac. It was not curly cherry but a really nice piece that I got at my 2 week course at the Center for Furniture Craftsmanship. It really has a nice look to it.

-- "Don't let the perfect be the enemy of the good." Voltaire

View harum's profile

harum

216 posts in 1106 days


#2 posted 08-12-2015 03:00 PM

Thanks Ellen! I have tried shellac seal coat followed by a thin coat of tung oil. It looked like pure shellac, except a bit more depth and color. But after two weeks in garage and a day out in the backyard the grain raised and the tung oil can be scraped off with nails—an ugly sight. I guess the tung oil hasn’t cured completely after two weeks in a hot garage and, besides, it’s quite hygroscopic.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."

View ellen35's profile

ellen35

2724 posts in 2895 days


#3 posted 08-12-2015 10:37 PM

Pure tung oil will never dry… try mixing it with mineral spirits as a drying agent.
I did the final “sanding” with a piece of rolled up paper bag just to give it a sheen.

-- "Don't let the perfect be the enemy of the good." Voltaire

View harum's profile

harum

216 posts in 1106 days


#4 posted 08-15-2015 04:16 AM

Yes, thanks! The question is where to get mineral spirits these days rather than “low-odor”, “low VOC” concoctions they now call “mineral spirits” that can ruin your project.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."

View harum's profile

harum

216 posts in 1106 days


#5 posted 08-22-2015 02:57 PM

Another coat of pure tung oil hasn’t changes the appearance of the cherry board, neither the color, nor the grain “depth”. My conclusion so far: pure tung oil brings out no chatoyance in curly cherry. When the oil is wet, the chatoyance is strong and deep, too blotchy though. When the oil is dry the chatoyance is gone, dark color and blotchiness remains. Maybe I should have coat the oil with varnish, but I want to abandon pure tung oil in favor of shellacs, which give nice chatoyance with no blotching. Someone has suggested Royal Lac, a modified shellac resistant to moisture and heat.

-- "If you're not counting the ripples when throwing pebbles in the water, you're wasting your time."

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