Paint 1/25/22

Science with Richard Bleil

The original woodwork has been painted with a thick heavy paint. Even what remains of the original floor has been painted white. My friend fears that I will burn my house down (or my hair off) because she knows I purchased a heat gun to strip the paint from the floors and original woodwork to see if I can resurrect it.

Paint is a fascinating substance. It consists of three major components, the pigment, the binder and the solvent. The pigment is what gives it its color. It works by absorbing all wavelengths of light except those that give rise to its specific color. The light of the wavelengths in its color is reflected rather than absorbed. It’s like getting a box of mixed chocolate and glazed donuts, but there’s always that one person that will steal all of the chocolate donuts. All you’re left with is the glazed.

Some years ago, it was not uncommon that lead salts were used as paint pigments. These salts have the two most desirable traits in a pigment, namely, they’re appealing in color, and they are stable, meaning they won’t fade in time. Unfortunately, lead compounds tend to have a mildly sweet flavor (which is why children will eat paint chips in old homes) and are heavy metal poisons (so if you see your child eating paint, get them tested as a simple blood test will reveal if there is a problem). This house is old enough that it would not really surprise me if there was lead in the paint, so I’ll have to be extra careful in removing it. A simple test with sodium sulfide will reveal if there is lead or not, as lead sulfide turns dark brown nearly to the point of black. Actually, this just occurred to me as I write this blog. I’ll have to get some sodium sulfide. It smells like rotten eggs. I’ll keep it in the kitchen.

The binder is what holds the paint to the surface, be it a wall, canvas or glass. In old paintings, the binder was a thick oil, which never dries actually. Technically, paintings from the Renaissance are still drying today. I’ve always wanted to paint with oils, but usually when I do a painting (yes, I paint) I work with acrylics. Acrylic is a polymer, a kind of plastic not unlike the acrylic used in fingernails. This flows as a “monomer”, small individual molecules that form the plastic by reacting and bonding to each other to form very long chain molecules. These long-chain molecules will wrap around each other becoming highly viscous (resistant to flow) and eventually harden. On a surface, this means that the paint is actually a form of plastic with embedded pigments. This is why heat guns (set at a low enough temperature so as not to burn the house down) is effective at stripping these paints. Basically, it is melting the plastic making it gooey and messy but easy to scrape off.

But the monomers and pigments need to be in a solvent prior to application to keep them fluid and easy to spread. This is actually an interesting example of a solution where the solvent is not the most abundant components (many chemistry books define solvents as the most abundant component, but this is inaccurate as it’s simply the “delivery mechanism”). A good solvent will remain liquid (in a closed container), be inexpensive, will dry quickly and will hopefully be non-toxic. Water is a decent solvent, it’s safe, inexpensive, non-toxic but might take a while to dry. When I was young, they always warned people not to paint unless the windows are open, and the room is “well ventilated”. The paints were smelly and often used solvents like toluene, the solvent used in model paints that people sniff to get high. It causes brain damage over time, but what a ride. Or so I’m told. Actually, today “huffing” is a thing which might also seem like a more or less safe high, but it, too, causes brain damage. Basically, anything that gets you high will have serious consequences on your brain and central nervous system, which is why I never indulged. Besides, isn’t life interesting enough without them?

Okay, soapbox speech is over. But seriously, don’t do drugs. Okay, NOW it’s over. Of course, another important thing about paint is to get the mix correct. Paint is not a true solution (all true solutions are actually clear). It’s what we call a suspension, which means that in time it will settle out. But if there is too much solvent, the paint will be too runny and difficult to apply. Not enough pigment and the color will lack vibrancy. Too much binder and the paint will be gloppy and won’t apply smoothly. Some years ago, the father of a friend of mine was working with a company to develop a new kind of printer that spritzes small amounts of ink on the paper, a printer that became known as an “ink jet” printer. I was a chemistry student then, early in my undergraduate training when he was explaining it to me but complained that they couldn’t get the mix correct. Seems like it was always too much causing bleeding and poor print quality, or too little and it blocked the jet portals. I simply said, “why don’t you change the solvent?” He looked at me, wide-eyed, saying “there are different solvents?” Interestingly, I may have made a significant impact on printer technology. Not interestingly, I didn’t get any monetary compensation for my contribution.


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