Blackening of steel is not done with Acid based solutions. Bluing or blackening in all forms is an accelerated rusting or oxidation and subsequent staining. The most common types of bluing are as follows:
Black Oxide Bluing "hot bluing"
Corrosive solids consisting of sodium hydroxide and sodium nitrite, mixed with not acidic chemicals for penetration and color. Run at 292 degrees.
Slow Rust Bluing
Non acidic, non toxic rusting agents. Heated to 150 degrees, applied, boiled at 212 degrees, carded and repeated.
Damascus Finishing
Non acidic, non toxic rusting agents. Heated to 100 degrees, applied, steamed at 100 degrees, carded and repeated. Boiled once in a mordant bath at 212 degrees.
Hot bluing of damascus or any soldered barrels will immediately or eventually destroy a set of barrels. The temperature and caustic solutions will attack the lead in the solder and break it down, destroying the bond.
I have not seen any evidence of the caustic affecting the welds in a Damascus pattern.
Hot blued barrels need to be completely resoldered prior to finishing.
Determining hot blued soldered barrels is fairly easy. They usually will not "ring". Exposed solder generally will appear white and crystalized.
Damascus barrels blackened by the "slow rust" process can readily be refinished to black and white, with the correct process.
The Damascus finishing process is the least invasive of all types of metal finishing. Using the mildest chemicals and lowest conversion temperatures. The patterns are a natural conversion of the steel and iron. The contrast, depth, color and patina, are more from technique rather than chemically induced.
Brad
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