Bichromate of Potash and Van Dyck Crystals

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Bichromate of Potash (Potassium Dichromate) is one of the most important chemicals historically used in woodworking. Rather than dying the fibers (as with aniline dyes) or putting pigment particles on the surface (as with all "stains") it reacts with the natural tannin in the wood to produce a deep rich walnut brown. The depth of the color that can be achieved is stunning. Comes as a powder and can be mixed in varying strengths with warm water to produce varying color intensities. Oak (rich golden browns) and mahogany (rich "Georgian" reds) are two which respond particularly well. Note: Bichromate of Potash is toxic. Read the instructions carefully and take all sensible precautions. Use a mask and gloves when handling it.

Van Dyck Crystals are a traditional, natural, water-based wood dye made from walnut husks with which different depths of brown can be achieved. It can be used to not only color but to shade or darken certain areas on the wood surface. Dissolve in warm water to the needed strength. Different shades can be obtained by adding water soluble wood stains.

See below for more information. Also used as a traditional brown calligraphy ink ("walnut ink") and often called "black walnut crystals" when used like that - the "black" refers to the black walnut husks it is made from rather than the ink color.
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Traditional, Natural Wood Coloring
The deep, rich color of 17th and 18th century antique furniture is due partly to the age of the furniture, but also, crucially, to the use of specific natural coloring techniques by the original finishers. Replaced in the early 20th century by the advent of aniline dyes, these techniques and materials are used today in antique restoration and mixed-species finishing like marquetry and parquet. Two examples of these traditional techniques are Van Dyke Crystals (a natural material made from walnut husks), and Bichromate of Potash, or potassium dichromate.

NOTE: Caution, Bichromate of Potash is highly toxic. Adequate precautions must be taken when mixing and handling. Do not inhale the powder or expose your skin to the liquid. Use a particle mask and gloves when handling.

Click Here to Download a PDF* for more information on finishing. (*Note: Requires Adobe Acrobat Reader)
Click Here to Download a PDF* for a Material Safety Data Sheet (Bichromate of Potash). (*Note: Requires Adobe Acrobat Reader)
Click Here to Download a PDF* for a Material Safety Data Sheet (Van Dyke Crystals). (*Note: Requires Adobe Acrobat Reader)

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  • potash-potassium dichromate

    Chris Jewett, 9/27/2016 The potassium dichromate adds a rich warmth to the walnut I am applying it to. The clients loved it and it is easy to mix, store and use
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