Seems like the topic of matching antique brass comes up from time to time on this group. Brass can be colored chemicly to achieve an antiqued color or patina. Below is a post I saved from rec.guns many years ago.
The Coloring of Brass by Royce W. Beal written on 17 March 1995 specifically for the readers of the rec.guns newsgroup. questions should be directed to me at snipped-for-privacy@CC.USU.EDU
Read this entire essay before attempting any one treatment. If you choose to just "cut and paste" part of this, please make sure you get the safety instructions and warnings after the recipes. Under no circumstances do I consider myself liable for any accidents which occur while using any of these chemicals. Also, I do not consider myself an expert in this field and am still doing research for the FAQ. This will be a temporary article. Because I am still experimenting, I cannot vouch for all of these colors. Concentrations and conditions DO matter. (Concentration is more important than actual volume, so if you want to use less, make sure that you use proportionately less of each ingredient) If you want good results follow the recipes closely. Above all it is important that the brass surfaces be clean. This means an extra hour or so in the tumbler for the cases and then touch them only sparingly. I have tried to collate recipes which will require the acquisition of the more common chemicals. I have also tried to steer clear of the really hazardous arsenic and cyanide salts (which you probably can't get anyway) If you feel that you've been cheated by this, please refer to the references section of this report and find the books for yourself in any well stocked library. It is my understanding that these are all surface coatings and should not damage or weaken the brass. Obviously you will want to do this treatment with unprimed brass. DO NOT USE METAL UTENSILS (ok maybe stainless steel) Glass or Plastic containers are the preference. If you are really worried about what this is going to do to your brass, refer again to the reference section below.
TIFFANY GREEN: Copper Sulfate.................8 ounces Ammonium Chloride..............4 ounces S odium Chloride................4 ounces Zinc Chloride..................1 ounce Acetic Acid....................2 ounces Water..........................1 gallon
VERDE: Copper Nitrate.................16 ounces Ammonium Chloride..............4 ounces Acetic Acid....................1 quart Water..........................1 gallon
GREEN: Iron ( ferric) Nitrate.........2 ounces ( Fe(III)(NO3)3) Sodium Hyposulphite............8 ounces Water..........................1 gallon (use at boiling temperatu re, brass can be immersed or the solution may be "painted" on)
HARDWARE GREEN: Iron (ferric) Nitrate..........1 ounce (Fe(III)(NO3)3) Sodium Thiosulfate.............6 ounces Water..........................1 gallon (use at 160F)
RED: Iron (ferric) Nitrate..........6 ounces (Fe(III)(NO3)3) Sodium hyposulphite............6 ounces Water..........................1 gallon (use at 170F will speed up this reaction)
BLUE: Sodium Hyposulphite............8 ounces Lead Acetate...................4 ounces Water..........................1 gallon (use at boiling temperature) or Lead Acetate...................2 to 4 ounces Sodium Thiosulfate.............8 ounces Acetic Acid....................4 ounces Water..........................1 gallon (use at 180F. This color will change if not lacquered [DO NOT LACQUER FIREARM CARTRIDGES] Take your chances with the color change.)
BLUE BLACK: Copper Carbonate...............1 pound Ammonium Hydroxide.............1 quart Water. .........................3 quarts (Add the water after the carbonate and hydroxide have been mixed. There must be excess Copper Carbonate. Use at 175F. This color can be fixed (made more permanent) by quickly dipping in a 2.5% Sodium Hydroxide solution.)
BLACK: Ammonium Hydrosulfide...........2.25 ounces Potassium sulfide...............1 ounce Water...........................1 gallon (use at room temperature or COOLER for best results)
BROWN: Potassium Chlorate..............5.5 ounces Nickel Sulfate..................2.75 ounces Copper Sulfate..................24 ounces Water...........................1 gallon (use at boiling temperature)
SAFETY:
- NEVER taste any of these chemicals.
- Keep very far out of the reach of children.
- Most Nitrates are good oxidizing agents and should not be stored with anything flammable.
- Acetic Acid has a VERY strong pungent odor. Use in well ventilated areas. This acid can be airborne in vapor form. If you feel that you have breathed enough of it to feel uncomfortable, leave the area and drink a carbonated soft drink. "Have a Coke" Do not underestimate this chemical.
- Many of these chemicals may stain your skin or clothing. Wear rubber gloves and protective clothing including glasses of some sort.
- Steam can cause serious burns. Solutions of salts can actually exceed the boiling point of water. The steam from these solutions can be very dangerous. BE CAREFUL WITH STEAM AND BOILING SOLUTIONS.
- Feel free to change concentrations for experimentation purposes but do not change the ingredients in any one recipe.
- Always be fully awake and alert around chemicals.
CONVERSIONS AND INTERPRETATIONS: Ounces are assumably troy ounces, even when dealing with liquids or solutions. Do not use fluid ounces.
1 ounce = 31.103 grams = 480 grains 1 quart = 0.25 gallon = 946.4 mL 1 gallon = 3.785 LREFERENCES:
Meyer, Walter R. title: Plating and Finishing Guidebook ninth edition - 1940 pp.72-75 (cited)
Metal Finishing Guidebook twenty-eighth edition - 1960 article by Hall, Nathaniel title: Coloring of Metals pp. 477-479 (cited)
Krause, Hugo title: Metal Coloring and Finishing (not cited)
Hiorns, A. H. title: Metal Coloring (not cited)
Field, S and Bonney, S.R. title: Chemical Coloring of Metals (not cited)
-Royce