Corrosion on stained glass is commonly referred to as white mold. It appears on the lead or solder lines, leaving the stained glass piece spotted and unattractive. The corrosion or white mold is frequently the result of flux residue that was not thoroughly removed.
One method used to remove the corrosion is to scrub the art glass piece with cleanser. This will remove the corrosion, but it may also cause scratches on the glass.
The best way I have found for removing the corrosion is to use baking soda. Baking soda is not as abrasive as a cleanser and will not scratch the glass.
You will need a small scrub brush or very fine steel wool. First, dampen the scrub brush or steel wool with water. Then liberally sprinkle baking soda over the piece. Using the dampened scrub brush or steel wool, scrub the glass piece vertically, horizontally and in a circular motion.
Once all the corrosion has been scrubbed off, thoroughly rinse off the baking soda and dry the art glass piece. If the piece had a patina finish, you may have to re-patina the piece. This will depend on how much corrosion had accumulation on the piece.
After the piece is completely dry, use a finishing compound to protect and polish the art glass piece.
This process works very well, though it takes time, work and reapplying finishes. If you have a stained glass piece with corrosion, you really do not have a choice. For future reference, you can avoid corrosion from occurring by properly removing flux when constructing your next piece.
The common cause of corrosion is flux. Never leave flux on a piece for more than a few hours. There are a variety of commercial flux removers that you can use. Be sure to follow manufacturers’ directions.
Using baking soda and dish soap is an alternative for commercial flux removers. First, sprinkle the piece with baking soda, then apply a small amount of dish soap to the piece. With a soft, damp scrub brush using a circular motion to scrub the piece. Rinse with water and then do the other side.
After the piece has been cleaned and rinsed with water, pat the piece dry with a soft clean cloth and let it air dry. Once it is completely dry, patina can be applied. The last step is to apply finishing compound to both sides.
Do not rush the cleaning and finishing. A good cleaning and finishing will save you time, work and expense later.