A. Coat with a high-temp paint (see. Fig. 1 at the beginning of this article). These high-temp paints can handle the temperatures used for aluminum brazing, and present a non-bonding surface for the Mg vapors when they cool down and condense on those coated surfaces. One such manufacturer, Glyptol Inc., in Massachusetts has been providing such coatings for a number of years.
When the furnace hot-zone is removed from the vacuum-furnace chamber, the coated walls can be scraped with a non-metallic scraper (or a bronze tool), and the condensed Mg will come out without too much effort. The painted surface may also be scrubbed with abrasive cloth materials to remove the Mg, but re-painting of damaged areas may be required.
B. Coat with a high-temp brazing stop-off. Some brazing shops have used some of the commercially available brazing stop-offs to coat their aluminum-brazing vacuum-furnace walls to prevent the Mg from sticking to the furnace walls, and have reported much success with it. Because of the proprietary nature of all brazing stop-off materials, it is strongly recommended to evaluate different commercial stop-off materials to find out which one works for you.
3. High-temp furnace burn-out. Heat up empty contaminated furnace to high enough temp to volatilize the Mg coating on the walls, thus “burning” the Mg off those surfaces. Be careful with this procedure, since the walls of the furnace must become hot enough to cause the Mg to volatilize. Experimentation is required to find out what kind of “burn-out” cycle will work in your furnace.
4. “Flaming Newspaper” technique. NOT RECOMMENDED! Believe it or not, some people have actually rolled up a newspaper tightly, ignited the end of it (like a torch), thrown it into the furnace chamber and quickly locked the furnace door so that the flame would ignite the Mg and quickly burn it. This kind of foolish action is EXTREMELY dangerous, and I have heard that at least one death has resulted from it.