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a video going into details on what the differences are between dye and pigment stains. It also tells you how both react to different kinds of wood (e.g., maple vs. oak). If you buy a can of stain off the shelf, try to stir it with a paint stick. If there's sludge on the bottom and little color on the top, it's pigment only. If there's no sludge, it's dye only. And if there's both sludge and strong color on the upper part of the stick, it's a bit of both. The can won't tell you (and the customer service is unlikely to know, as I found out).
There are three major types of products that color wood. 1. Dye 2. Pigment 3. Chemical Dye Dyes are chemicals that dissolve into its solvent,that could be water, alcohol, petroleum distillates, or oil. You can find dyes at concentrates as liquids (such as TransTint), powders that you dissolve (Lockwood), or even as part of a canned stain (Minwax Golden Oak). Dyes are dissolved and do not settle out. If you are looking at a can of stain and stir with a paint stick, you will not find any solids at the bottom of the can. You can control the color saturation by the amount by which it is diluted. You can start with a full dose, then dilute part of it to various degrees (half, quarter, etc.) to get the amount of color you want. Keep careful records so you can replicate it if you are making your own dye solutions. Dyes give a very clear coloring, but are more prone to fading over time. Lightfast is more of a relative term. If you get the color too dark, you can wipe with the appropriate solvent and pull out some of the color or you can even add another color to adjust darkness, neutralize (e.g., too red, too yellow, etc.) Pigment Pigments are powders that are suspended in a carrier. Pigments lodge in the grain and pores of the wood (and the sanding marks if you are not careful). And as such, pigments tend to blotch on certain woods due to their varying porousness. Pigments will settle out to the bottom and if you stir a pigmented stain with a paint stick, you will find a muddy residue at the bottom of the can. You can control the color saturation by the amount you wipe off. You can also buy pigments in powder form to make your own products, you can even smudge some powder onto problem spots and lock in place with a spray. Or add pigments on a finishing wiping cloth and pad in some color. These methods are used in touchup. Pigments are usually more lightfast than dyes. Chemicals Chemicals change the color of the wood by chemical reaction. Generally these are acids or alkalis such as ammonia (fumes), lye, potassium permanganate, bichromate of potash, potassium dichromate, iron dissolved in vinegar (iron acetate). The resulting color is not reflected in the color of the solution and the same solution may work differently (or not at all) on different woods due to their different composition. Heartwood and sapwood may also color differently even on the same board. You "control" the color saturation by trials, length of treatment, and in some cases the concentration of the chemical. There are several disadvantages to chemical stains It's a "ready, fire, aim" approach. Run trials. but in many cases, it's going to do what it's going to do and you are not going to stop it. Wood from one tree may not color the same as wood from another tree. Many of these chemicals are toxic or caustic to your skin, eyes, and lungs. Do research and use carefully and with PPE and ventilation. They may be hard to find a place to purchase. A good application of some of these is in inlay work where a chemical may color some of the species, but not others. Again, research, choose woods carefully, and run a trial before slapping on and ruining weeks of work. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&ved=2ahUKEwitk4DxgczcAhWk6YMKHVmTBbsQFjALegQIABAC&url=http%3A%2F%2Femgw.org%2FResources%2FDocuments%2FPapers%20and%20Articles%2FChemicalStains.pdf&usg=AOvVaw0l3kGfTTJa7DxfVTrNs7oH An oddball colorant that does not really fit neatly into any of the above is Gilsonite, AKA asphaltic tar. You can use roofing tar dissolved in paint thinner/mineral spirits to get a mid- to dark-brown color. This is the colorant used in some "walnut" Danish Oil products. It's a nice color that is hard to get with the above. (c) 2018 Keith Mealy
I was working on a finishing presentation last week. I thought I had a reference in one of my books on decoding Minwax stains into pigment, dye, or both. I don't use them too much any more, but I happened to use some Golden Oak a few weeks ago. I've had good luck with it on red oak and I know it's dye based. But I could not find the reference. After much looking, I wrote to Minwax tech support and asked. They told me all they used were pigments. Idiot. I wrote to Bob Flexner to see if he had ever done the catalog. Low and behold, it's in this week's blog entry. I guess I'm his "woodworking friend." https://www.popularwoodworking.com/woodworking-blogs/flexner-on-finishing-woodworking-blogs/is-there-pigment-or-dye-in-minwax-stains-does-it-matter