Woodworker's Journal 2011-35-Winter, страница 26

Pigment Stains

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pigment s t a i n a can of ordi

ut the prop ? look no f nary house

erties of urther than paint.

Pigments are the most common coloring agents in all stains. Well over 90% of all commercial stains contain pigments, and some, including all exterior stains, contain no other colorant. Understanding what pigments are, how they behave, and how you can make them work for you is probably the single most important thing I can share with you about staining wood. For starters, I'll give away the secret ending: pigment stain is actually just thin paint.

What is Pigment?

Let's begin with the basics. Pigment is essentially ground-up dirt. Colorful dirt, admittedly, but still ground-up dirt. Imagine that you were to take a handful of dirt from the ground and sprinkle it into a glass of water. Give it a quick stir and you have a glass of muddy water. In other words,

you've made something that will cause brown stains on light colored wood. Mind you, the dirt did not dissolve; it merely became suspended in the water. Your proof is that if you let it sit a while, the dirt will settle to the bottom and you will have to stir it again. That is your first clue in identifying pigment stains; the pigment can settle. If a can of stain says that you must stir it before (and often during) use, it contains pigment. Sometimes you can scrape some of the settled pigment from the bottom of a can that has sat for too long and see what it looks like congealed. The only ones that don't require stirring are the gels that are too thick to let the pigment settle or stains that contain only dye. (For more on dye stains, see page 30.) Unlike dyes, pigments will not fade in the sun, so they are the exclusive coloring agent in exterior or interior/exterior stains.

How Pigments Color Wood

If we were to smear some of our mud mixture onto a piece of light colored wood, it would make it more brown. The dirt would find pores, rough spots and even sanding scratches in which to lodge. That's what happens with pigment stains too. In fact, the more porous the wood is, and the coarser the sandpaper we use before staining, the more sites pigment finds to lodge and the darker the stain becomes. That's why end grain, summer wood in softwoods and the large pores of cathedral grain in oak and ash take in so much stain. The pigment finds nooks and crannies to inhabit, just like the butter in the old English muffin commercials.

On the other hand, if you wipe a pigment stain onto a finely sanded piece of rock maple, a wood with very small, tight pores, almost all of it will wipe right back