SECRETS OF PAINT AND STAIN CHEMISTRY

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Lye, in either its solid crystalline form or in solution is a lethal poison that can burn. your skin (it takes a little time to act, so a quick wash-off will prevent a serious burn). But just a tiny spatter can permanently damage eyes before you get to a water faucet to rinse it out. So, unventilated side-guard-equipped safety glasses are mandatory, and long rubber gloves and sturdy, long-sleeve outerwear are strongly advised.

Be sure you pour crystalline lye into water—not the other way around, lest you cause it to erupt and spatter all over you. If you have small children around the place, use all the lye you buy make. Don't ever keep a half—used container around the house—even on a high shelf.

On the positive side, lye is an honest, straight-forward caustic agent. It warns you of danger—by stinging. Further, its action is good old-fashioned inorganic chemistry, incorporating no complex hydrocarbons that can exert a subtle, lingering effect on human health or on air or water quality. The soapy, stripped-paint/lye residue must be disposed of properly (especially if the paint contains lead—which makes it toxic waste). But lye itself is neutralized almost instantly on contact with natural acids in the soil or ground water (not that you should pour used stripping solution—or any paint or solvent—out in the backyard, down the drain, into the sewer, or in your septic tank).

One technique is to make a saturated solution and paint it on, keeping the surface constantly wet till the old paint releases. Or, you can purchase lye water mixed with an inert (silica) gel, so it goes on thick and stays moist by itself.

Old paint and stripper are scraped off, and what's left of the solution and paint residue is neutralized with boric acid or vinegar and water. The scrapings are stashed in a corner of the shop to evaporate. Then, the sloppy residue is bagged in plastic (it will eat holes in most anything else—especially aluminum cans), tagged, and taken to the toxic-waste holding shed at your dump or transfer station, whence it will be hauled to a licensed toxic-waste facility.

POLYMERS NEW AND OLD

The most ultramodern, hi-tech paints are concocted using sophisticated polymer chemistry. Polymer is a techno-intimidating word, but is just a chemist's term for plastic. Synthesized plastics have been around since Bakelite was invented in 1903.

But natural plastics have been used to make varnishes a lot longer. The natural protein, casein, in milk (concentrated when the curds of cottage cheese are separated from whey), is a polymer used as a binder in old-fashioned milk paint. The polymer in ordinary shellac is lac, a transparent, yellow resin that's exuded by an insect. Common pine tree sap consists of turpentine and rosin, a naturally hard resin once used to make varnish.

Chemically, polymers consists of long chains of simple compounds (monomers) that slide past one another to varying degrees, making the plastic ...well, plastic so it will mold into any shape and retain its resiliency. In paint, the polymer serves as a binder to which fillers and pigments are added. For example, to mix modern house paint, white chalk or another benign filler plus pigments are added to a liquid resin. Originally the polymer used was latex—rubber—largely replaced by synthetics these days, but originally made from the milky sap of tropical American trees.

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