Is potassium dichromate worth the risk?
A highly toxic chemical is said to create amazing effects in finishing. April 4, 2000
I've heard that potassium dichromate, used as a treatment for mahogany, brings out the color and grain to a very deep, rich appearance. Can anyone give me info on what it does, how to use it and where to get it?
You can get it from chemical supply houses and photography supply houses. A word of caution though: it is very toxic and I believe carcinogenic, so great care is required in its use. A vapor mask and good quality gloves are a must.
George Frank, a renowned finisher, wrote about its use on mahogany and I was interseted in using it myself, but the toxic nature and not being able to find a complete explanation of how to use it safely has kept me from trying it.
I myself have played with this chemical and have found the results not worth the hassle. You can get the same color with dye stains.
Bob Niemeyer, forum moderator
I have used this chemical on mahogany and I thought the results to be very dramatic. Besides, it was fun -- but you should wear the safety equipment.
The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).
Comment from contributor H:
I run a finishing shop in southern British Columbia, and our clients are always asking for "old looking" fir.
I have found that potassium dichromate is well worth it. Because it is a chemical reaction (oxidizing agent) it does not have the same effect as a wiping stain. It retains the same relationship between the winter and summer growth. A stain will darken the soft summer growth more than the winter growth. Potassium dichromate will darken the two equally, resulting in a very even and very convincing "old" look.
George Frank also said that gasoline is a very dangerous substance, and yet, we all use it safely. It is important to be safe and wear gloves.
As for concentration: try 3 grams of potassium dichromate for 1 litre of water (warm is better). This is a very light colour change. Go as high as 40 grams per litre for a very rich dark colour (beautiful).
Even though it is a chemical reaction, you still must sand all parts equally to ensure even colour. And be aware that it does not touch hemlock, so make sure you are not mixing spieces.
Comment from contributor M:
I am a violin maker and use potassium dichromate on my violins. It needs sunlight to create a chemical reaction to make the wood flame pop out. That creates the dark stripes on the violin family instruments. The reaction is with the tannin in the woods, mainly hard woods. The stronger the mix and the longer exposure to direct sunlight will make it darker.
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