This is a dangerous chemical which I intend to use on some curly cherry. (It is reported to darken but eliminate blotching – see FW #140, 0. 130 by Chris Minick). Researching the safe use of the chemical has raised more questions than answers so far, including the following:
(1) wear a good respirator – (Questions – is it the crystals – dust, or is it the vapor from the mixed solution (water), or both) which are harmful? The MSDS says it doesn’t evaporate significantly. Exactly what kind of respirator – the description of “good” doesn’t help me a lot, nor does the MSDS language “a half-face dust/mist repirator … specified by the appropriate regulatory agency or respirator supplier…”
(2) Should the acid be neutralized after application? If so, what do you use to neutralize it?
(3) Neutralized or not, does the chemical retain it’s harmful effects after it dries on the wood? i.e. can you sand the wood safely after application? (It is mixed with water, so you’re going to have raised grain.)
Any practical help would be greatly appreciated. Chairwright
Replies
I first read about this stuff years ago in an old finishing book, but backed away when I learned how potentially dangerous it was.
Just because a technique is old doesn't necessarily mean that we should resurrect it. Years ago, they used mercury in the process of blocking hats (hence the term "mad hatter"). Maybe someone around these forums can suggest a modern (and safer) equivalent that will give similar results.
I assume that, as an alternative, you have considered a coat of dewaxed shellac (or Seal Coat from Zinsser) to prevent blotching.
As far as respirators are concerned, I would think a "good" respirator for this would be one rated for organic vapors, which would also protect you from dust. With the OSHA presence, most metropolitan areas have a store that specializes in safety equipment, and will be able to help. I have gone to the the counter any number of times, told them what I was working with, they looked it up, and then told me specifically which respirator model I needed.
Incidentally, I have a respirator that can take a variety of cartidges/filters, so this is not a matter of buying a whole new set up.
As you run down this road, I hope you will tell us what you did, and how it came out.
[Edit: sorry, Paul, I hadn't read the other thread you had on curly cherry.]
I seem to remember a couple of great posts and discussions, including pictures, of finishing using potassium dichromate. A large table comes to mind? Try do a search and see if you can find them.
As far as the blotching goes, there are other much safer ways to approach that problem, so if that's the only reason you're considering the PD, I'd vote no. Find a copy of Jeff Jewitt's "Great Wood Finishes" -- he outlines, with instructions and pictures, 3 different ways to finish cherry and avoid the blotching problem.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Another proud member of the "I Rocked With ToolDoc Club" .... :>)
Edited 5/31/2004 12:00 pm ET by forestgirl
Virtually all chromium compounds are toxic. Dichromate is not an acid, its an oxidizer. You can't neutralize it. Can possibly change it to an insoluble salt, but I'm not enough of a chemist to know how. The dust is toxic. I would not sand it. One crystal in about a cubic yard of air is the toxicity threshold. It continues to react with the wood. This can take years or longer. I know of violins treated with it that have continued to darken for many decades. If you need a respirator, that assumes you have some airborne particles. They're going to settle onto nearby surfaces. You now have a contaminated workplace. Chances are that if you use care, you're not going to get it all over creation. But, why deal with the risk of dropping the jar or whatever. A yellow-orange dye or strong tea or turmeric or saffron or a host of other things can achieve about the same effect safely. If you absolutely must use it, only open the container outdoors. I did use a little of it years ago, but as soon as I knew the facts, I disposed of it. Not for amateur use. And in my opinion, any professional should likewise avoid it. I wouldn't knowingly sell something treated with it to one of my customers. You never know who's going to put what in their mouth.
I have used it for years with no problem. I consulted with my Father-In-Law who is a Chemical Engineer and a college prfessor. He says that the greatly diluted form that we would use is about as dangerous as household bleach. A pound of the stuff is another matter but an ounce in a quart of vinegar is no problem. You still need to be careful and follow prudent saftey precautions.
el papa: Did you sand it when you used it? As per Paul S, did you observe the wood darkening for years,a nd does your Father-In-Law chemical engineer think it is dangerous in the wood?
p.s. The responses remind me of a great Far Side cartoon. A hapless dog, the accused (in this case potassium dichromate), is on the witness stand, beside him stands his lawyer, another dog. The judge, all the jurors, and all the reporters and public are all cats. The lawyer dog pleads to the jury: "A cat killer? Is this the face of a cat killer? A cat chaser maybe, but hey, who isn't!" Chairwright
I do not dry-sand it but I usually do apply the first coat of stain or finish with steel wool, I hope you understand why. And "NO" it has not continued to darken over the years. I asked my Pa-In-Law about this before hand, he said "BS". This man is a serious professional and answers his questions carefully. His take was that it would be inert after it dried and was under several coats of finish especially in the tiny, tiny amount used. Again think of the tiny amount you would deal with if you took an ounce, mixed it into a quart of vinegar and used a 1/4 of a cup of that mixture to darken a large piece of furniture (a little dab will do you).
Does full-strength ammonia continue to darken A&C furniture that was fumed circa 1900? No, of course not and for the same reason. Furthermore that full strength ammonia they used way back when was a lot more dangerous (and powerful-and harder to control) chemical then potassium dichromate.
I read an article about potassium dichromate in some magazine (FWW?) and the author made several claims about it including that it would continue to darken over the years. My Father-In-Law read the article for me and thought many of the facts made by the author were knaive and "unsupported". After years of using it (and doing my own research) I agree. Be careful with any chemical you use!
Edited 6/1/2004 1:41 am ET by el papa
I presume you apply the stain with steel wool to scrape off the raised grain. Do you dampen the surface to raise the grain and dry sand it before you apply the potassium dichromate?
First of all let me say this..."Water is the right thing to mix it with not vinegar as I had stated earlier, a serious mistake that I take full credit for." I don't know what I was thinking. Here is my plan for success with "Potash".
Sand completely and remove all traces of glue but do not, repeat, do not use any filler yet. If you do it will turn bright orange and not brown like the wood. I never saw a need to raise the grain but I suppose you could. Test on scrap because it can be dilluted (with water) for a lighter appearance. Too much is too dark and nobody wants that. Also be aware that sap wood will sometimes not turn brown at all but rather it will be yellow or pale orange. I assume these areas have less tanic acid in them and therefore react differently-or not at all. Apply with long rubber gloves, safety glasses and ventillation. Allow to dry before handling. I found that the "hang over" from potash was two-fold, a tiny fuzzy orange crystal "stuff" on the edges of the wood and a slightly raised grain. To overcome these I use steel wool to apply whatever stain I want over it. The brown color it leaves is rather "odd" and not natural in appearance so stain is mandatory. Fill holes afterward and apply second coat of stain. From this step on there is nothing special to report.
I mainly use it for repairs of fumed oak A&C pieces of furniture. Lots of A&C style bungalows locally and the young people who buy them find some real junk furniture to be restored (suckers). I have found no other way to make oak really look old and fumed no matter how many layers of stain or dyes used. I have also used it on cherry (a thin dillution), walnut (turns it jet black) and once on maple (nothing else would match). It will not work on wood that has been previously finished.
Oh, and no reason to pour the old stuff on your garden as it has no shelf life and will last a long, long time in a closed (and labeled) container.
So your point is "the solution to pollution is dilution". I learned that phrase from someone in the cleaning industry. It's basically true - how the world works.
I once asked a friend who is a PhD research chemist the same question, and got a similar answer. As long as you are protected from dust (can't remember the size in microns, but it was at least an order of magnitude bigger than the .3 my respirator is rated for) and don't do anything careless or stupid before it is sealed under a film finish, the hazards are lower than the radon in your basement--the quantities involved are just too small.
I bought some years ago and didn't care for what it did to oak, but still have it in my shop. After talking with the friend, I left it in the original container and two heavy-duty ziplock bags with the label clearly showing, but may yet pull it out again.
Now, for some serious fun, try potassium permanganate and nitric acid on quilted maple, but that is a different thread....
/jvs
I fooled around with some of those trick over 20 years ago. I got the best results from Lye. or caustic soda. There was a red devil brand that is sold in the grocery stores for about $1 the last time I bought it. It seem to work best on woods that were naturally red. Mahogany turned a very nioce deep richer brown, Padauk turned purple like E Inidian rosewood.
Lye is a strong alkali. If you use it be sure to follow directions, like don't mix it in an aluminum container. If you don't like the end results just wipe it down with vinegar. This will totally reverse what you just did.
just to make this clear I would like to say. THIS IS NOT WORTH THE TIME AND EFFORT.
First, It is so hard to get on without showing overlap streaks.
Second, You will be doing this after you have sanded and are ready for finish. Whenever you apply this stuff, it will be the equivelent of hosing down the project with water, so there will be so much lifted grain that you will have to re-sand, which will enevitably lead tos danding off the affected surface color which means you will have to wet it down again, and then you will be faced with the question of
Three. Do I neturalize this stuff? Will it cause problems with the finish if I don't. How many weeks do I need to wait before the wood gets dry enough to finish?
Your hand is just reaching out for this bucket of worms. Do I need to tell you more.
I came to the conclusion that it was cheaper to use rosewood than to double the finish time, and add that much anxiety.
One of the best ways to darken without stain is Sunlight. Just beware there are lots of birds flying around out there, and too much can cause surface checks.
I use to put mahogany out for a day when I knew the weather would be good, but this can lead to problems too. When I set things out the sun would be at X and for each hour the sun moves 15 degrees. You have to make sure ther won't be any shadows later. I would estimate that one day in direct sunlight is equal to six months of natural oxidation.
Do you think potassium dichromate, which is described as an oxidizer, would present the same or worse CAN - O - WORMS than the lye?
If it is a water soluable oxidizer. My best guess would be yes. I would not move forward with it without doing some test. Maybe someone else will come forward with some tricks that I could not find.
Can you give me more to work with? what are you making, and what are you calling blotchey?
Any grain change will cause a color difference under certain lighting.
I never show a customer wood under flourescent lighting, I think wood looks best under polorized light. Or stated diferently from one or multiple point sources.
As light is reflected off of wood fibers, it bounces better at certain angles, kind of like a pool ball bouncing off of the rail. If the light strikes the wood at the corect recroprical angle the fiber really reflects the light best. The more you diviate from that the more the wood will absorbe the light. There is a geological term for this, I think it is chatoyancy. If this is what you are seeing don't try to cover it up. Show your customer that they should pay extra for their good fortune.
Unless you are making a chair out of this, then you should be looking for strait grained wood. so the legs won't break off because of short-grain situations.
It's a cherry table top. I use extra wide cherry boards and make tavern tables with bookmatched boards with the most interesting and extraordinary grain I can find. You can see some of them on my website, http://www.chairwright.com This particular table I'm thinking about using the potassium dichromate (pd) on is 41" wide made of 2 bookmatched cherry boards. In cherry boards this wide it is not unusual to find several different grain patterns or types of grain. One predominant, but not uniform over this particular table top is is curly, a/k/a tiger stripe, grain. It looks like 3 dimensional hills and valleys just like curly maple and it shows chatoyancy in that grain, which I do not want to lose. The customer understands all of this and has paid extra. In additon to the curly grain there is also some regular old cherry grain and there is some wormy grain in the middle and edges, but not sapwood (by the way it is all kiln dried so the worms are long gone), and some graying discoleration from the beginning of old age in the middle, which doesn't bother me at all because it makes a nice flame pattern running most the length of the table now that it's bookmatched. What I'm trying to avoid is blotching in the regular old cherry grain which may detract from the curly. I got the pd idea from an article by Chris Minick in FW#140, p. 130 (Feb, 2000) - represented there to darken nicely without the inevitable blotches of stains and dyes. Considering all the posts and thinking about it the last couple of days, the thing which concerns me the most is sanding after it is dried. I'm sure, since it is water based, that it will raise the grain. If this stuff is as wicked as many say, then when I sand it, I'd be making my shop unsafe for others present there, that's not a good thing, and I will avoid that at all costs. (However, I also know that most potentially dangerous chemicals can be used safely. ) I've sprayed on dyes, water based, alcohol based, and oil based before, and it's not a bad solution. I've also used a spit coat of dewaxed shellac to partially fill the problem pores before dying, staining, and tinting, and that's not a bad solution either. It just seemed to me that the pd would be a quick and sure fix - the Holy Grail! You know what they say, if something seems too good to be true ... Thanks for your help. Chairwright
HEre is the MSDS sheet for it.
Any time you have a chemical you are not sure about. Put the name in quotes and the add + MSDS. These sheets should be read so you know EXACTLY what to do if you have a problem.Kevin Arceneaux
Visit the Lone Wolf Activities for MS Trainsimulator at http://www.3dtrains.com
Kevin: I did read the MSDS but did not find it particularly helpful beyond the obvious precautions. I'm looking for more practical information, such as whether it is safe to dry sand the stuff after application.
Those trains are neat. The BNSF double (mainly coal) line from Wyoming to Chicago runs about 100 yards from my shop - unobstructed view.
Chairwright,
I've been using potassium bichromate since the early 70's, for pieces that are inlaid, primarily. Color intensity increases with the strength of the solution you use. 1/2tsp/qt of water will give a light brown, 4 tsp/qt tends toward a dark red . Too much will be almost black. The effect varies with individual pcs of wood (maybe reacting with amt of tannin?) so practice on a scrap from what you intend to use it on. Works on cherry, mahogany, and oak that I know of. Does not work on sapwood.
It is dissolved in water, so I sand to 180, wipe with wet cloth, let dry, then sand with 220. Then apply your solution. It's important to maintain a wet edge, it shows lap marks badly if you go over a dry area again. After it's dry, I then steel wool to knock down any whiskers. I was taught to follow up with a coat of oil to pop any figure (you may call this blotchy) then continue with finish of choice.
You are already aware of the issues of safety with this chemical. Maybe I'm already doomed to cancer from using this stuff,I don't know. I won't know if it's from the spray fumes I breathed while spraying thistles as a kid on the farm. Or maybe it will be the bug spray I was covered with, thinning apples in the orchard one summer after high school. Or the asbestos laden sheetrock compound I sanded when I was doing remodeling work. Carlyle Lynch was an advocate of using potash, as he called it. He worked with it daily in making the blueprints he sold. I saw him pour the used solution on his rhubarb plants! When I questioned the safety of doing this, his reply was, that it was potassium. I told him it was the chromium that worried me. He did die from cancer. I think he was in his 70's when he passed.
Now I use a water based aniline dye in place of potash where I can. I think the dye is more colorfast, as well as safer to use. In my experience, potash will lighten as it ages, not continue to darken. Cherry that starts out dark red will go to a warm reddish amber in 10-15 yrs. It seems to me that potash bleaches out, but of course the cherry will darken with time, so it averages out. It is a very natural looking color, as it is transparent.
Regards,
Ray
I used PD on 3 sets of french storm doors, in mahogany. My procedure was to raise the grain first with water, and then carefully sand it back with 320. Then the PD, wiped on (outside), standing upwind. I used long rubber gloves, and a largish rag to avoid lap marks. I then brushed on a coat of thinned spar varnish. I sanded that back lightly, to smooth, then 2 more coats of full strength spar varnish. They have been on my house for 5 years now, without being touched.
Couple of points. Mix in a glass jar. Use warm water to mix. Tap hot is fine. Mix it outside, so any dust blows away from you.
I tried it on some cherry, but was not fond of the color I achieved. It deepens and enriches the mahogany. On cherry, it just looked a bit muddy, and darker. It has not darkened on the doors over time. It has held its color nicely.
I would not think it affected blotching on cherry. I think the blotching comes from rising and falling grain on the surface. If you like the color on cherry, I think I would raise the grain, sand it back, then apply the PD. Then I would shoot one or two coats of a dewaxed shellac, or a laq. sealer, and sand back only after the second coat was dry. I would not expect very much grain raising at all. I use a lot of transtint, cut with water, on figured woods. Esp. the honey amber color, as a base. I find that if I raise the grain first, and then sand it back, the smallish amount of water applied with a water based dye raies the grain very little, esp. if I have been able to hand plane the surface to start.
I have chosen not use use the PD on interior furn. On the doors I felt safe with the notion that they would not be eaten by children or pets. But on a table, I don't know enough chenistry to feel comfortable. HEnce my decision. Were I to do a door again, I would consider its use as the color is perfect.
Alan
Alan
http://www.alanturnerfurnituremaker.com
Thanks for all the replies. This is what I learned from all of you and a friend of mine who is a chemical engineer. Potassium dichromate is a salt and an oxidizer. It is K2Cr2O7. The chromium part is toxic. I can't be neutralized. Top coating the wood should render the piece non-toxic and the small amount which I would use probably makes it an acceptable risk in terms of my health, but it is still probably not safe for a food surface. So it is out for my table. In fact, in my shop it is out period - it's just not worth the worry and the potential liability issues. What happens if Billy Bob decides to strip and refinish the table 20 years from now and his fingers start falling off, even if it is because he is unusually sensitive to chromium. I think a good trial lawyer would love to take that case against me! No thank you! Chairwright
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