If todays Belgian blue is the same as sold by Herter's many years ago & I think it is, it is an express rust blue. The rust is brought on rapidly by applying the solution, hot, to bbls having the temperature of boiling water. It also contains mercuric chloride which is quite poisinous. I used it years ago, but not on damascus. I have no idea how it would respond to the treatment to bring out the pattern.
This is not in anyway related to trappers dye, or to spotting blues such as Prussian Blue, commonly used in hand fitting parts.
