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Blueing is a process where steel is more or less protected against rust by applying a layer of oxidation. This layer is extremely thin (2.5 micrometers; 0.0001 inch)
andprovides minimal protection against rust unless it is treated with wax or oil.
Blueing can be achieved in many ways:
  • Birchwood Casey’s „Gun Blue” and „Plum Brown” are simple methods for blueing steel but I consider this method unsuitable for the restoration of antique firearms.
  • Temper-blueing is fairly simple too: first the steel is polished „in the white” , then heated under a layer of sand. When rising the temperature the steel first will turn ocher and after a while deep blue. This method may alter the structure of the steel making the gun unsafe to fire. Besides: the layer of oxide is extremely thin and not wear resisting.
  • Coppering is a technique where steel is electroplated with a thin layer of copper and chemically colored.
  • Black nickeling is an electroplating technique too and far superior. Nickel adheres very strongly to steel and is very hard making this method very durable.
  • Rust blueing is a old technique where steel is covered with a very thin layer of magnetite, the black oxide of iron (Fe3O4).

Many techniques to achieve perfect blueing are described in detail in R.H. Angier’s book „FIREARM BLUEING AND BROWNING” but most recipes mention extremely toxic chemicals like „Mercuric Chloride”, „Fuming Nitric Acid”, „Sulphuric Acid” and even „White Arsenic” (As4O6) making most of them impractical for general and domestic use. Fortunately some of these recipes are quite simple and require non hazardous chemicals, in particular some rust blueing techniques. By searching the internet lots of recipes can be found and during this quest it became clear that most gunsmiths used private and secret formulas. Although not tested by me, I even found a recipe where rust was provoked using urine!

For re-blueing pinfire weapons it is reasonable to choose a technique that was used in the era of their production. Between 1830 and 1890 rust blueing was often used by individual gunsmiths and small armories. This technique is very time consuming and requires craftmanship but few specialized tools are required.

The procedure for rust blueing is as follows:
  • First all surfaces will have to be polished. Highly polished surfaces will result in a brilliant finish while a dull surface will yield a non reflecting coating. Mind: all remaining scratches, dents and pitting will be clearly visible in the end result. For an optimal end result, it is of the utmost importance to carry out this process with much care.
  • The next stage in rust blueing is degreasing. Even the smallest traces of grease will result in an uneven reaction with the oxidizing agent causing a blotchy unsatisfactory end result.

In the course of time the original blueing of antique firearms changes into a brownish patina. Due to intensive use this layer will wear down leaving the metal unprotected agains rust. In order to preserve the characteristics of an antique weapon, this appearance should not be altered.