I got an interesting call about a finish problem the other day from a dear friend who is an expert antique restorer, among his many other talents. It was a bit grisly, but nonetheless an interesting poser. I thought I’d share it with you.
“I picked up a piece of 1950s furniture from a crime scene in which a murder had been committed,” he began. “The mother of the victim wants the piece restored. It had been covered with luminol, a blood detection chemical used by criminologists, and there is a definite stain on the wood. In the finish itself is the sort of white discoloration you get from a wet towel that’s been sitting on lacquer too long. Under that is a dark stain in the wood itself, and the finish has developed fine cracks.”
He was planning to refinish the piece, but wanted to know if the luminol created any toxicity issues, what in it caused the stains, and what methods, if any, were needed to remove it from the wood. The white stain was, of course, not an issue, since it would come off when he removed the finish, but removing the dark stain in the wood was a bigger challenge.
While he was still on the phone, I looked up both the technical data and MSDS [Material Safety Data Sheet] for luminol. First synthesized in 1902, it’s a complex aromatic hydrocarbon that, through chemiluminescence, glows bright blue when it comes in contact with the iron in blood hemoglobin. On the positive side, it’s not particularly toxic or dangerous.
It is normally dissolved in a glycol ether and mixed with an activator, usually hydrogen peroxide, then sprayed evenly on the surface. Both the glycol ether and the peroxide can cause white stains in many finishes, and the peroxide can also cause dark stains in many woods.
The fix is to remove the finish, wash the wood with alcohol or a glycol ether to remove any luminol residue, then reverse the dark stains by washing the raw, lightly sanded wood with a 10% solution of oxalic acid. Once the acid dries, usually overnight, the salt residue is removed or neutralized before a new finish is applied.