Clean the metal with denatured alcohol to remove any grease or grime. This is wiped on with a clean, lint-free rag and dries quickly. The surface of the metal must be clean and dry to ensure the patina forms correctly.
Fill the kiln with charcoal, using only pure charcoal without additives for food grilling. Light the charcoal and let it burn until all areas appear evenly heated. Move some of the pieces aside using a rake, and bury the metal in the charcoal.
Allow the metal to bake for three hours, then remove it with tongs or a shovel. Be careful, as the metal will be extremely hot. Cool for 48 to 72 hours before handling.
Mix sulfurated potash with ammonium chloride in a large bowl. The solution encourages oxidation of the metal and quickly creates a patina that looks almost identical to a traditional charcoal-blue finish.
Add the distilled water, stirring until all ingredients have dissolved. This takes between 30 seconds and one minute.
Brush the mixture on the metal with a lint-free rag, sponge or soft paintbrush. The solution will oxidize the metal, creating a blue patina. Allow to dry before handling. Repeat if a deeper blue is desired.