Q: I have an oil painting in need of cleaning, not restoration. It's not an heirloom, and it's not very valuable. It was an auction buy, for $100. But I like it and think it would be much improved by cleaning. It's about 12½ inches by 34 inches. I think the signature is "Pettie Stotlemeyer," with no date. The painting seems quite old. What do you suggest I do?

Jefferson, Md.

A: Cleaning an old oil painting without damaging it is a very tricky undertaking — “one of the most demanding areas of painting conservation,” according to an overview published by the Smithsonian Museum Conservation Institute.

Jessica Johnson, head of conservation for the institute, said in a phone interview that when a painting isn’t valuable enough to warrant professional cleaning, she normally recommends doing nothing. “If it’s dirty, it’s not going to get worse,” she said. “If you clean it and do the wrong thing, there’s a chance you could affect it badly.”

However, provided the paint isn’t flaking off, you can probably remove loose dust without risking damage by following advice from the Smithsonian: Wash and dry your hands, then set the painting on a clean surface. Tip the painting so it angles toward you at the top and the dust you brush off doesn’t land on the painting. To remove the dust, use a soft brush about one to two inches wide with natural-hair bristles. Don’t use a dust cloth: Threads might catch on a rough spot on the painting. A feather duster or a stiff brush are also out; they can scratch. With the soft brush, you can gently brush off the surface, working from the top down or across the painting. If the painting has a matte surface, be especially careful not to brush for too long or with too much pressure so you don’t burnish the surface, making it shinier in spots.

Many oil paintings have a varnish coating installed to make the colors more saturated and the sheen more even and to protect the paint from dirt and dust. Unfortunately, varnish tends to yellow and darken with age. Cleaning can remove the varnish, which might make the colors in the painting look brighter. But solvents that remove varnish may also damage paint. Figuring out which solvent is safe to use on a specific painting requires a testing protocol and an understanding of art history, chemistry and materials. There’s a reason professional conservators spend years in training. If you were to attempt the cleaning on your own, it might create the damage Johnson warns against.

Various websites recommend a couple of cleaning methods that they say are safe, including brushing away dust with a fine-bristle brush or an old shaving brush, and dabbing away oily grime with wads of white bread. But even brushing away dust, as the Smithsonian recommends, wouldn’t be safe if the paint is brittle and coming loose. And the bread trick can leave crumbs, which invite insects.

It’s also possible to buy solvents that dissolve various varnishes and then test them to see whether they work without picking up any color from the painting. Winsor & Newton, which makes artist paints, has instructions under the page “How to remove varnish from an oil painting” on its website, Winsornewton.com, but even that begins with this warning: “It would be a tragedy to damage a valuable painting by trying to remove the varnish if you have not had any experience in varnish removal. The best advice is simply to take it to a conservator.”

If you want to do that, the American Institute for Conservation and the Foundation for Advancement in Conservation have a “find a conservator” feature on the website Culturalheritage.org. Type in your Zip code, choose how many miles you are willing to travel to take your painting to a conservator, and select “paintings” in the search box. Then scan the results for conservators who do treatment.

Most conservators do an initial consultation without charge. They’ll evaluate the condition of your painting and explain their proposed treatment, with an estimate of the cost. You then decide whether to go ahead with that work.

Even though you think your painting needs only cleaning, not restoration, a pro might spot details you haven’t noticed. Alex Volkonsky, owner of Sable Fine Art Restoration in Bethesda, Md., (202-568-2704; sablerestoration.com), looked at the pictures you sent and said he thinks there could be some cracking of the paint layer. If a hands-on evaluation at his studio in Silver Spring, Md., confirmed that, he would recommend relining the painting — a process that involves attaching new canvas to the back. He would also test cleaning methods to find what works without causing damage, then replace the varnish to help stabilize the paint. Volkonsky is not listed on the American Institute for Conservation’s website, but he has had years of training, including five years at the Corcoran School of the Arts & Design at George Washington University. All together, he estimated the treatments he listed might take him eight to 10 hours and would cost $320 to $400, less than many conservators charge. For a painting you love, that might be a worthwhile investment — and safer than attempting it on your own.

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