I find it interesting how mahogany turns to a dark color with exposure to sunlight. Unfortunately, it sands off during the finishing process and if the finish has UV inhibitors, it takes a long time for the dark color to return. So, I was trying to think of a way do hasten the darkening process after sanding. Does anyone think some time in a tanning bed would make it darken?
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My wife and I attended Ben Hobb's furniture class, each making a beautiful end table. Before finishing we were given the option of using "potassium dichloride"(sp) to make the mahogany accelerate developing it's patina. I used the potassium, wife did not. This chemical does give a really nice "aged mahogany" look!
When I returned home I tried to buy some of the potassium for future use (Ben had it in flake form, much like shellac flakes). I could not find it locally or in any of my woodworking catalogs, so quit trying. The tables are both finished with oil and shellac, and my wife's is still not as "aged" as mine, but the difference is much less pronounced than when we made them-now several years ago.
I also believe wet sanding with BLO/turpentine and then shellac will give a really nice patina.
http://www.hobbsfurniture.com
Pete
That's potassium dichromate, and it's nasty, nasty stuff. It can burn your eyes and skin, it has high acute toxicity if taken internally, it's carcinogenic and mutagenic, and it's a long-lasting environmental pollutant. There's no reason to use it these days.
-Steve
So as you say their is no reason to use this anymore, then I take it you have a way to make the wood look like it would if you used it? If not then their is a reason to use it. It is just (in your opinion, and most likely a lot of other peoples) that the use is outweighed by the down side of the nasty chemical in question.
Doug
Various recipes have been published over the years. See, for example, Darrell Peart's article in the Dec 2007 Popular Woodworking for a simple version.
You really ought to try using Google. It will open up a world of information....
-Steve
Hay, I am not the one that made the blanket statement that their is NO reason to use this method. I happen to disagree with the comment. Their is a reason, and I HAVE looked into other options and they ALL have drawbacks. It happens that for looks this is one of the best/easiest options. That being said it has some really nasty side effects (as you listed). I just did not like the flat statement that their is NO reason to still use it. I will agree that their are some good reasons not to use it but that is different then no reason to use something. Their are pluses and minuses to a lot of things, and choosing which of which you can live with is the hard part.
Doug
Yes, there are advantages to using potassium dichromate in woodworking.
Just like there are advantages to owning slaves.
-Steve
Yes its dangerous stuff. But if you take the proper precautions with mask, eye protection and gloves (and a bit of common sense!), its no dangerous than any other chemical or finish. Since you brush it on, there is little danger of contact with the afore mentioned precautions. I'd rather use it than lacquer.David Marks has used it for a number of projects on Wood Works.I got some from a photographer friend. Its also labelled as potassium bichromate.Everyone has to decide what risks they are willing to take. Even sawdust can be hazardous without the proper precautions. (and far more common to overlook those precautions) Just use a little care and common sense.
Below is the MSDS on Potassium Dichromate.Known carcenogenic, also noted as such by the PDRC.(Note that almost everything is a known carcenogenic in PDRC. I'm waiting for the warnings regarding sex.)No mention made of being teratogenic. Were it, there would be. Your offspring are safe.So, use proper precautions when handling, mix no more than you need and don't drink it. GFS CHEMICALS, INC.
P.O. Box 245 Powell, OH 43065
740-881-5501(Tel.) 740-881-5989(Fax)
1-800-424-9300(Chemtrec 24Hr. Info.)
MATERIAL SAFETY DATA SHEET POTASSIUM DICHROMATE
CHEMICAL NAME & SYNONYMS DOT CLASS SARA TITLE 313
Potassium Dichromate; Potassium Bichromate 6.1/II Yes-Cr Cmpds.
TSCA listed - Yes
FORMULA REPORTABLE QUANTITY F.W. CAS#
K 2Cr 2O 7 4.54 kg 294.19 7778-50-9PHYSICAL DATA
Density 2.69; Melting point 398°C; decomposes 500°C; Solubility in water 4.9 g/100 ml at 0°C;
102 g/100 ml at 100°C; pH (5% solution about 3.7).APPEARANCE & ODOR
Red-orange crystalline powder. Odorless.REACTIVITY & CONDITIONS TO AVOID
Stable. Avoid breathing dust and skin or eye contact. Incompatible with reducing agents,
alcohols, many organic solvents. Environmental hazard.FIRE HAZARDS
May react vigorously with certain reducing agents or organic substances with possible resultant
fire. Firefighters wear SCBA. NFPA # 4-0-3.EXTINGUISHER FLASHPOINT LEL UEL
Water Spray N/A N/A N/AHEALTH HAZARDS
Toxic internally, inhalation may cause destruction of mucous membranes. Skin contact may cause irritation. LD 50 (oral-rat) 25 mg/kg; ACGIH TLV: TWA .05 mg (CrO 3)/m 3; OSHA PEL 0.1 mg (CrO 3)/m 3.
ACGIH A1 - confirmed human carcinogen; NTP - known carcinogen. Warning: This product contains a chemical (hexavalent chromium compounds) known to the state of California to cause cancer.SPECIAL PRECAUTIONS
Use dust mask, rubber gloves and goggles to handle in quantity. Avoid all contact.FIRST AID
Wash thoroughly after use. For eye contact, wash thoroughly with water and get medical attention if irritation persists. If swallowed, give water or milk and get immediate medical attention. Do not induce vomiting unless directed by a physician.SPILLS & LEAKS
Wash up with water. Disposal to hazardous waste. Environmental hazard.
Leon
The MSDS at Fisher Scientific lists it as both mutagenic and teratogenic (see below). As for its carcinogenicity, hexavalent chromium is on the California Prop. 65 list. While I'm not a big fan of that legislation (I think it has a lot of problems, actually), the list itself is a pretty good one, and quite conservative; out of the tens of thousands of chemicals in use, only about 600 are on the list.
I assure you that I'm not exactly the Chicken Little type. I've done my research. Hexavalent chromium is exceptionally bad stuff.
-Steve
From the Fisher MSDS:
Teratogenicity: Oral, rat: TDLo = 1 gm/kg (female 0-19 day(s) after conception) Specific Developmental Abnormalities - musculoskeletal system.; Oral, mouse: TDLo = 1 gm/kg (female 20 day(s) pre-mating) Effects on Embryo or Fetus - extra-embryonic structures (e.g., placenta, umbilical cord) and Effects on Embryo or Fetus - fetotoxicity (except death, e.g., stunted fetus). Reproductive Effects: Oral, rat: TDLo = 525 mg/kg (female 21 day(s) after conception) Fertility - pre-implantation mortality (e.g. reduction in number of implants per female; total number of implants per corpora lutea) and Fertility - post-implantation mortality (e.g. dead and/or resorbed implants per total number of implants). Mutagenicity: Micronucleus Test: Human, Lymphocyte = 300 ug/L.; Morphological Transformation: Human, Fibroblast = 200 nmol/L.; DNA Damage: Human, Fibroblast = 500 nmol/L.; Unscheduled DNA Synthesis: Human, Fibroblast = 50 umol/L.; DNA Inhibition: Human, Fibroblast = 100 umol/L.; DNA Inhibition: Human, HeLa cell = 13 umol/L.; Mutation Test Systems - not otherwise specified: Human, Fibroblast = 100 umol/L.
Steve:Interesting that the MSDS from one vendor list it as teratogenic, one doesn't.I'd assumed an MSDS was an MSDS, and we've just had a demonstration of what ASSUME means.I do wonder what research those figures are based on, as I'd never heard of dichromate being teratogenic, just dangerous to inhale/ingest. Leon
"I'd assumed an MSDS was an MSDS..."
I think it's mostly a matter of when it was published. New info and all that. I tend to trust the MSDS's published by the chemical companies as representing the latest and greatest, so to speak.
-Steve
I think it's mostly a matter of when it was published. New info and all that. I tend to trust the MSDS's published by the chemical companies as representing the latest and greatest, so to speak.
______________Yep, I'd agree, problem was, the two MSDSs cited were both from chemical supply houses.The one I cited did not have a publication date shown, IIRC.Go figure.Leon
"Unfortunately, it sands off during the finishing process..."
That doesn't quite make sense to me. If you completed all of the "bare wood" work, left the piece out in the sun for a few days (or however long it takes), and then applied the finish, wouldn't that work? Any sanding done to the finish itself shouldn't affect the wood.
-Steve
Waiting a few days (more like a few weeks) would absolutely work, but I'd rather not wait that long.
quickstep,
I believe Rob Millard had a process to age the mahogany using lime. There maybe some info on his website... http://americanfederalperiod.com/tambour.htm
Edited 1/2/2008 8:24 pm ET by BG
Well, the trick is to have all of your sanding done before you put it out, and hope a big flock of blackbirds don't fly over.
I have put parts out in the Sun, and when it is bright, it can happen as fast as 4 ~ 6 hrs. One thing to not overlook, is where the Sun will be after say 4 hrs. I had some parts placed where they would cast a shadow on other parts close by, and the shaded part will always be behind in the oxidation, or shading, relative to the other parts.
If you are using solid wood, there may be a chance of causing some warping / cupping by heating one side more than the other, if you change the MC by essentially cooking off more moisture from one side than the other.
If you want to try a chemical rout. Try using lye, or caustic soda. It cam be found in the store as drain cleaner. It is hard to get an even job though. If you want to undo what you have gotten, just wipe it with vinegar, and this will reverse what the lye has done. Try it on padauk to see a wood that really reacts.
Regardless of the feud between Steve and Doug, you can certainly find and use potassium dichromate. It will certainly accomplish the task you wish for mahogany. You should, as Steve suggests, use EXTREME caution, as his warnings are all valid. However, it could be said that similar dangers exist in operating woodworking machinery, or driving a car, or.......well, you get the point. Be careful if you decide to use potassium dichromate, and use maximum safety protocols. It is an excellent way to get the patina you desire, albeit a dangerous one.
Jeff
"However, it could be said that similar dangers exist in operating woodworking machinery..."
But that's exactly my point. The dangers are not similar. Using a table saw is dangerous (you might cut your fingers off). Fuming with ammonia is dangerous (you might get a bad burn). But neither of those activities will give you cancer. And neither will cause genetic damage in your unborn children. Worst of all, when you pour that spent dichromate solution down the drain, you're leaving the world a legacy of contamination that will outlive you by a very long time. It's this last aspect, the fact that there's really no way to dispose of it safely, that is of the greatest concern. You can protect yourself from direct exposure, but once it's out in the environment, there's nothing you can do.
Everyone knows about the dangers of lead and mercury. Hexavalent chromium (the "active ingredient" in potassium dichromate) doesn't make the headlines as much, but it's at least as bad and in some ways worse. The OSHA exposure limits for Cr6+ are much lower than those for mercury and lead, for example.
-Steve
For the record, I know for a fact that Ben does not use Potassium Dichromate anymore, he mainly uses analine dyes. He in fact discouraged me from trying it just yesterday, there are many safer options.
Calvin Hobbs (Ben Hobbs, Jr.)
Quickstep,
I have often thought about the tanning bed idea and wondered if it would work. I've never been to a tanning salon, so I don't know if the bed gives off heat, but if it did, I'd be careful what I put in there, for fear of it warping.
I once darkened a firescreen panel in the sun since I was sure it wouldn't warp. With most things, though it would be risky to place them in the sun, or anywhere heat would be applied unevenly (like the hinged leaf on a card table)
The best way to darken mahogany is a chemical treatment. While you could dye it, the underlying wood would continue to darken and at some future date your piece will be too dark. On the other hand, pieces that I have used chemicals on have remained very color stable for at least 10 years.
Potassium dichromate is a chemical that was used for this, and may still be, but it seemed too dangerous to me, so I have never used it and can't say how color stable it is.
Lye, as in drain cleaner, works very well, but is a bit dangerous too.
I now use hydrated lime purchased at the garden store. It is as safe to work with as an anline dye and imparts a beautiful color to mahogany. There are some downsides to (there always are) It is predictable, but not really versatile, in that it only makes one color, red; only the shade can be varied. It also can ruin a project if you don't experiment with it and get the ratio of lime to water right, because it can over darken a piece, and there is no way to remove the color ( I did try once with a two part bleach and it did okay, but the brilliance of the wood was also "removed" and didn't come back when refinished) It will over darken crotch mahogany. If you're not careful it will over darken swirl mahogany. Finally, it is somewhat tricky to apply. I spray it on, being careful to work from the bottom up, because if a spot of lime hits an untreated area it will leave a mark, that can only be gotten out by wet sanding the spot with the lime mixture. Despite those few pitfalls, it is a great way to color mahogany.
Below is a link that more or less repeats what I just said here, but you can see the results of the lime on a project.
http://americanfederalperiod.com/finishing.htm
Rob Millard
Edited 1/13/2008 2:40 pm ET by RMillard
Potassium dichromate works in two separate ways to color wood:
1) Chromic acid is a strong oxidizer, and causes a chemical reaction in the wood.
2) The potassium dichromate is itself colored, and acts as a dye.
It should be possible to create an equivalent result by using separate oxidizers and dyes. Both sulfuric and nitric acids are strong oxidizing acids comparable in strength to chromic acid (and, although themselves hazardous at high concentrations, are much, much safer overall than chromic acid, with no long-term residual problems). Aniline dyes can be had in virtually any color, of course.
Hydrochloric (muriatic) acid, which you can get at the hardware store, is not an oxidizing acid, and won't have the same effect. Chlorine bleach and hydrogen peroxide are strong and relatively safe oxidizers, but they're not acidic, so the effect on wood might not be the same.
-Steve
So back to my point, it is nasty and dangerous, but we really do not have a perfect replacement. So their IS reason to consider using it, just as their are reasons (really good ones to) to consider NOT using it. Still this is something the user needs to decide for his/her informed self. Not to have dictated on him/her with a blanket statement that their is no reason to use it.
Note I never said to use it, I never said not to use it. I am not the one on this thread arguing either side, I just think that people in this supposedly free country should be allowed to make their own mind up.
Oh and the slavery issue comparison is so OVER the top that you should be ashamed of yourself for making it. And in this day and age you are taking a heck of a chance on offending people by using it. Just because you believe something does not make it so for the rest of the world. Something you may want to consider before making bold statements.
I will give you that In YOUR opinion the good benefits of using this are way outwayed buy the bad. To bad your other wise intelligent post was effect buy you attempt to may your (apparently informed) opinion out as fact. This is a problem a lot of people have. It would be nice to get ride of the gas engine to, but at this point all other options have down sides that are hard to live with. Same thing here. All the other options have down sides.
Doug
Hi, The sun is for free. I "stain" two woods in this way ; African Rosewood and Rhodesian Teak. After sanding i expose it to sun light then apply the first coat. Sand very lightly now , do not sand the finish off. I use a synthetic "sandpaper"- You would have them from 3M . The longer in the sun the darker it will become. If you use an oil base it will also darken in the sun after you have applied the first coat. Rhodesian Teak also darkens in colour when washed with a cloth dampened with thinners.
African Greetings
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