All Birchwood patinas are considered traditional patinas that will age or darken metal. These patinas are sold concentrated and should be diluted with distilled water (up to 50%) before use. M-20 is the same Black Antiquing Solution as M-24, but is made for an immersion (dipping) process. Normal dilution ratios would be 1:1, 2:1 or 3:1 (patina to distilled water). Using the solution too strong may cause problems.
For more information and help check out this awesome guide by Sculpt Nouveau *HERE*