Under the Soot: cleaning smoke damaged glass

We clean our share of dirty glass in the Conservation Lab at The Corning Museum of Glass, but occasionally we get some unusual requests. Recently, one of our colleagues brought us objects from his personal glass collection that withstood a house fire. Soot on glass artwork and food stains on bakeware may not be the most natural connection to make; however, our conservator instincts recognized that in both cases organic materials had been heated to high temperatures, so we started by revisiting an old blog about cleaning Pyrex.

To tackle this new problem, we wondered if we could use lower concentrations of sodium hydroxide if we soaked the objects for a short period. The surface of each object and the smoke deposits varied, so we needed to work flexibly– what worked for one object did not necessarily work for all. For example, we used a higher concentration of sodium hydroxide to loosen soot on some objects with sensitive surfaces so that we could soak for a shorter time and avoid vigorous brushing.

We worked object by object, gradually increasing soaking time and/or concentration of sodium hydroxide until we could remove the soot by swabbing or brushing gently. The general idea behind our process is: soak, test, assess, then adjust and repeat as necessary.

If you decide to try this at home, please do so safely, keeping in mind that contacting a conservator is always an option.

Supplies:

• Protective equipment: rubber or neoprene gloves, goggles, a smock
• Tap and distilled water
• Liquid detergent, preferably one with no artificial colors or scent
• Sodium hydroxide or lye (we used solid 100%)*
• Plastic tub
• Soft paper towels
• Synthetic brushes (natural hair may dissolve)
• Cotton swabs

*A few words of caution. Sodium hydroxide is caustic. It should never be ingested or inhaled and will burn the skin or eyes on contact. Work in a well-ventilated area and wear appropriate protective equipment. Please be sure to follow the manufacturer’s recommendations, see here for more details.

Method:

1. Put on the protective equipment (the gloves, goggles, and smock).

2. Test. Some types of surface decoration and adhesives can be sensitive to water. Consider contacting a conservator if you suspect cleaning might damage the piece. Otherwise test a small, inconspicuous area with a cotton swab wetted with water to make sure there are no surprises. Seeing a favorite vase transform from brightly painted to colorless before our eyes, while perhaps enjoyable in another context, is probably not the experience sought here.

3. Soap and water. While it is tempting to jump ahead to more aggressive cleaning methods, some objects can be cleaned successfully with just soap and water.

Fill a plastic tub with warm tap water and a few drops of liquid detergent. Place the object in the water bath and let stand for 1-2 minutes, then wipe the surface gently with a cotton swab to test whether the soot has loosened. The soot should come off the object readily and stubborn areas can be persuaded gently with brushes, swabs or paper towels.

• If effective, continue to brush or wipe until all soot is removed, then proceed to step 6
• If moderately effective, either soak for longer or proceed to the next step
• If ineffective, proceed to the next step

4. Sodium hydroxide in water. Start with a small amount—we started with about a teaspoon of 100% lye powder in a gallon of water—because you can always increase the concentration. Soak for 1 minute then test surface.

• If effective, brush or wipe until all soot is removed, then proceed to step 6
• If moderately effective, either soak longer or proceed to the next step
• If ineffective, proceed to the next step

5. Adjust the concentration of the solution by adding another half teaspoon of lye. Soak, test, assess. Repeat the process until the piece is clean.

6. Wash any sodium hydroxide off the surface with soap and water. Rinse with distilled water to prevent hard water spots.

Care and a little patience are well worth the result. After all, who doesn’t love clean glass and a dramatic set of before and after pictures? If you would like more information on our process, our findings were presented in a poster at the most recent ICOM-CC Glass and Ceramics conference in London.