Note: Due to current high workload, some services listed on this website may be temporarily unavailable. Particularly, we are currently not taking on restoration, re-bluing, or stock-making work, due to the high labour content required.
The main types of bluing we undertake in our workshop are the hot caustic bluing method, traditional rust bluing method and the Nitre Bluing (or Fire Bluing) for small parts. We can also do colour casing of some parts.
Overview of Bluing Operation
All metalwork to be blued must be first brought up to an acceptable finished state. This would include removal of any rust spots and pitting, rough machining, and any other surface imperfections using the most professional and efficient methods possible. The quality of workmanship by the ‘metal’ polisher must be of the highest standard to avoid common mistakes by the amateur, such as ‘running’ the engraving or the edges of flat surfaces.
The hot dip bluing process (briefly) involves degreasing of the parts before immersion in a hot (280° F) caustic solution until the right depth of colour is obtained. The process does not alter the surface finish. The parts are then rinsed cold, then boiled out in hot water mix to remove any traces of the caustic ‘salts’ that may have worked into small recesses in the parts. The parts are then submersed in special finishing oil and allowed to cool, before draining off and allowing to ‘stand’ overnight. The bluing process is usually complete within a few hours.
The traditional Rust bluing method is a lot slower and very labour intensive. Briefly, the process involves degreasing the parts, boiling out in hot water to heat the parts and remove any foreign residues. Chemical solution is then carefully swabbed onto the parts and they are then suspended in a special ‘rusting chamber’ where the temperature and humidity is controlled for about 2 hours. This allows a red rusting to form on the parts and also slightly etches the surface of the steel. Using a stronger solution, or increasing the temperature, humidity level or time spent in the rusting chamber can increase the degree of etching. Skill and practice must be used to achieve the right degree of etching. Too much can spoil the job. The parts are then boiled in hot water for 10-15 min. This changes the red rusting to black.
The parts are dried off, then the loose rust is ‘carded off’ with either a very fine wire wheel or ‘0000’ grade steel wool. Care must be taken at all times not to touch the parts by hand to avoid contamination with oil. The chemical solution is then swabbed onto the parts again and the cycle is repeated 4 or more times until the right depth of colour with an even finish is achieved.
Finally the parts are boiled out to neutralise the rusting, then they can be soaked in the finishing oil. The process can run over several days. It is usually more durable than caustic bluing.
Nitre Bluing (Fire bluing) is usually for smaller parts such as screw and pinheads, sight parts, triggers, etc.
Dry potassium Nitrate (Nitre) is carefully heated until it melts. The degreased parts are then quickly suspended into the molten chemical and watched carefully until the right colour change is reached.
The desired colours are often straw, purple, or iridescent blue.
The process takes only a few minutes or less depending on the size of the part. It is then quickly removed and either allowed to cool at room temperature or quenched in boiling water. If the part is air-cooled it must be dipped in boiling water to remove the dried chemical. The part can then be examined for any imperfections, then lightly oiled. The oxide (bluing) layer is very thin.
Parkerizing
The Parkerizing process is different from the bluing process (which is essentially a pre-rusting/ oxidising of the steel surface) in that Parkerizing is actually a manganese- phosphate coating that chemically bonds to the surface of the steel. The colour obtained is grey to dark grey/black depending largely on the hardness of the steel. Generally the softer the steel the darker the finished colour. For this reason you often get a different colour shade between the barrel and receiver or other ‘hardened parts’. Parkerizing bonds best onto a bead blasted surface, the finish is a matt non-glare coating, that is microscopically porous. This helps to hold rust preventing oils on the surface. Parkerizing has long been used as a military coating, and while not being as attractive to some as bluing, it is an excellent choice for hunting guns being far more durable than all of the types of bluing.
The process is usually complete within a few hours. At the end the parts are soaked in oil or dried. If dried they can quickly be painted, the Parkerizing acting as an excellent ‘primer’.
Note: Bluing and Parkerizing can only be applied to the carbon or chrome-moly type steels used in firearms, and sometimes castings. They will usually not work on stainless steels, although there are some exceptions.
Mil-Spec Coatings
A relatively new process which uses a spray-on ‘paint’, called “Moly Resin”, which has a phenolic resin base incorporating molybdenum disulphide (a superior lubricant), with a blend of additives. The process briefly involves cleaning the parts, followed by a light bead blasting. The coating is applied to a thickness of 0.0003″ to 0.0009″, and then the parts are ‘oven cured’ to 120-130° C. The colours available are dark grey/ black, flat black, semi gloss black, flat grey, flat green/olive, medium brown, flat tan/sand and ‘stainless’ silver. The combination of olive and two of the other colours can be applied in a camouflage pattern if desired. These coatings have passed extreme testing for resistance to saltwater atmosphere, acids and other chemicals. This is a cost effective method of metal protection for hunting guns, etc.
(Please note the service is contracted out.)
