I run across posts and articles in various places (including some articles in Fine Woodworking) that mention using potassium dichromate as a treatment to oxidize or color wood. I work with dangerous stuff for a living (I’m a chemistry professor) but I get really concerned when I see photos of someone wiping this stuff around in a woodworking shop. I’ve handled it often enough, even used to do classroom demonstrations with it, but this is a case where the problems outweigh the possible advantages by a pretty large measure. You can read in great detail about the toxicity and safety issues on the Material Safety Data Sheet (MSDS):
http://www.sciencelab.com/xMSDS-Potassium_chromate-9927403
The skinny is that potassium dichromate is toxic via the skin, the eyes, swallowing it and inhaling it. It is classed as a cancer-causing substance. Though it is not flammable itself, because it is a strong oxidizer it can cause combustible materials to ignite. Improperly handling this may contaminate your home, exposing family members. Also in the U.S., federal, state and local laws regulate its disposal, which is neither easy nor cheap–users are responsible for compliance. In my workplace, we often have to pay more for proper disposal of hazardous materials than the original cost of buying them. Working with materials like this requires an bunch of responsibilities that few woodworking shops are prepared for. Why go through that when there are a so many simpler, safer alternatives?
Replies
In general I agree with you, it would be rare occasions where a dye wont work at least as well, with dramatically less need for care, but occasionally there are circumstances where there aren't many alternatives. The one that comes to mind is the case of inlays, where the goal is to color the primary wood, but leave the inlays, typically low tannin woods such as holly or maple. You can't use a dye because it would also color the inlay. Protecting inlay from the dye, or stain, is not generally feasible--I've never got shellac protection to really work well, for example.
But, barring such situations, dyes will do at least as good a job at achieving realistic colors. There are some alternative chemical stains that may work to avoid coloring inlays, but the colors may not be as satisfactory.
Granted that all the above is true, the stuff is crystalline so that dust inhalation is unlikely. Gloves and common sense should take care of the rest.
It's interesting how many chemicals have become dangerous since the time when I studied Chemistry. Must be evolution in action :-)
On a serious note, ALL chemicals should be treated sensibly but not paranoically.
I've been using K2Cr2O7 for a long time to age cherry. I works better than "stains" and to me looks much better.
I have a degree in chemistry. I can see some people getting into trouble with a lot of finishing solvents and chemicals but with a little care the average woodworkere should be fine. I think most folks will just use what they can get at the local Rockler or woodcraft. BTW, I'm sure you know that you can get it from Fisher or VWR on a University discount pretty cheep.
My last graduation ceremony was in '74 so I doubt that I qualify for any University discounts plus being in the wrong country.
OTOH I still have excellent contacts and these things are not a problem.
I haven't yet tried chemical treatments apart from bleaching but I've got the chemicals lined up for the day when I do.
I have been researching potassium dichromate specifically for the application that Steve mentions - adding some color and depth to woods such as mahogany, cherry and walnut that have inlays. Thus far I have been too put off by the toxcisity of potassium dicrhomate to try it but I am also struggling with alternatives. Lye and hydrated lime are the two I have read about but the former is also pretty toxic and the latter seems to be unavailable. All I can find is some other sort of lime. (Have not tested it yet.)
As Steve mentions, sealing the inlay with shellac or lacquer does not work very well in my experience. Has anyone heard of other alternatives?
Thanks, Chris
Chris,
Lowe's has lime and so does Amazon.com (two I found in a quick google search). I think almost any garden center would have it, since it used to do something to soil. I have a couple of bags of it, one from Lowe's and another from a defunct garden chain called Frank's. If you want a small amount to try, email me through my website and I will send you some.
Rob Millard
http://www.americanfederalperiod.com
http://www.rlmillard.typepad.com
Lime source
Rob,
Thanks for the offer on the lime, if all else fails I will order some from Amazon. We don't have Lowes in downtown Chicago and I checked all the garden centers (Home Depot, Menards, etcl) and all they carried was "dolomite lime." Not sure exactly what the difference is but the package says it is "safer than hydrated lime." I will try it out and report back. I do have some lye so I will run a test with that as well.
BTW, do you know which woods either of the chemicals tends to color and which they do not effect? I know it is always a good idea to do some tests first but this info would be useful in planning the inlays.
Thanks much for the help and thanks for writing your great blog. I look forward to the next installment in the breakfront construction. I have picked up a lot of great tips and ideas from it.
Chris
Chris, I haven't actually
Chris,
I haven't actually tried to buy any lime in several years, but the Lowe's and Amazon websites show it. I have been told that pickling lime sold in grocery stores is the same thing, only refined to be food safe. I checked online and it seems to be true, but I have not tried it.
The lime works well on cherry, but not as well as lye. It seems to have a limited effect a walnut, which surprised me, since it is high in tanin, as evidenced by what it does to your hands. Red oak turns kind of green, which isn't a good thing. White oak takes on a very nice brown color (see attached photo)
I'm glad you like the blog. A new installment should be up by the end of the week.
Rob Millard
http://www.americanfederalperiod.com
http://www.rlmillard.typepad.com
Lime, Lye, etc.
Rob,
I tried to respond to your post but for some reason it was labeled as replying to the original poster. At any rate, per the other reply I posted I tried the lime I had and it did not seem to do much of anything to change the color of the mahogany. See pics in other post. I also tried some lye and it appears I mixed that one up too strong as the wood got really dark. What sort of concentration do you use and/or what sort of color change do you look for after the lye but before the top coat?
That little flip stop in your picture is neat and an unusual shape - is that a period detail or something you came up with?
Thanks
Chris
Source for Lime
Chris,
Today,I bought a package of Mrs. Wages pickling lime at Wal-Mart. I just finished trying it out and it works exactly like the lime I got from Lowe's and Franks. If anything it seems to work better, because it is very finely ground and stays in suspension longer. I have not top coated it, but I can't see any issues. I think any grocery store would have it or something similar.
Rob Millard
http://www.americanfederalperiod.com
http://www.rlmillard.typepad.com
Polychrome,
I agree.
I bought some and used it once on a test panel. Not only did the stuff scare me, it gave some inlays a wretched orange color.
Perhaps with more testing I could have overcome that problem, but nothing was going to make it safer. I had not thought about the disposal issue. I now use lime or lye. The lye is pretty nasty stuff, but the lime seems safe enough and neither poses a disposal concern. One is made for the garden and the other for the drain.
Rob Millard
Lye is Sodium Hydroxide or caustic soda. Lime is Calcium Oxide which reacts with water to form Calcium Hydroxide or quicklime.
Caustic soda is a very strong alkali, very soluble in water. Quicklime is a weaker alkali and much less soluble, hence its relative safety.
Please use gloves and do not try to dissolve lye in hot water. It gets hot when it dissolves and the water could boil, with painful results. Lye can form up to a 40% solution but you should never need more than a 10% solution except for clearing drains.
I hope this helps somebody sometime.
Lime Test
Rob,
I tried the lime I was able to find here in Chicago, Espoma Garden Lime that says it is pelletized dolomitic limestone, lime score 96. I mixed one heaping teaspoon to two cups warm water and shook it up until most, but not all, dissolved. I applied it to a test piece and it did not seem to change the color of the mahogany at all. The wide strip in the first photo had the lime applied and the narrow strip at the top is raw wood. The jar on the right is the lime solution which is rather brown. I expected it to be whiteish for some reason.
I also tried a test with Rooto household lye. I mixed that one level teaspoon to two cups water and got very different results. The second photo shows that test strip, again the wider one at the bottom. I am guessing that one will be way too dark when all is said and done.
I know the top coat will change the color some but I would be interested in any suggestions on what to look for here.
Thanks much.
Chris
Don't forget to rinse very well and then neutralise the soda with a solution of 2 parts vinegar + 1 part water. (and rinse well again).
Caustic soda is (was?) used in some paint removers.
Lime and Lye Sample
Rob,
Thanks much for all the advice. I suspected I was on the wrong track with that brown "lime" solution. I will keep looking for the correct sort of lime. I appreciate your offer to send me some but I hate to bother you and I am sure I can find it somewhere in this city of 3 million people. In the mean time I can always dillute down the lye solution I already made up. Your dedication to the lime really makes me want to try it out although I may just substitute a coat of blond shellac for the yellow dye and oil in the finishing schedule you discuss on your blog. I am only finishing a small picture frame at this point. If it was a bigger project I would try the whole schedule.
Thanks again for all your help both here and on the blog.
Chris
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