This is a reliable, domestically-produced room temperature blackening agent, Gun Blue solution, with a proven track record of sales on Mercari and other flea market sites (those with "ya" in their name). This Gun Blue solution is for bluing, a 200ml concentrate, and is a substitute for Birchwood Blue. The product is new and unused. It is contained in a Gun Blue solution-specific bottle (with a scale) that prevents leakage even during long-term storage. The parts in the product image are sample images of steel and zinc alloy parts for toy guns (made by Tokyo Marui) that have been blackened. Effective materials are HW (heavyweight resin), zinc alloy, brass, copper, and iron (steel). Basically, if the material is effective, it can be used on various products such as golf club heads, motorcycle parts, and automobile parts. In addition to normal bluing, this Gun Blue solution is also ideal for repairing scratches and peeling on zinc alloy parts of airsoft guns and model guns, where the base metal is exposed. For example, if you dip a cotton swab in the concentrate and apply it to the exposed base metal of the parts, it will dye black naturally, making it overwhelmingly more cost-effective than using a Gun Blue pen. If you polish the surface with sandpaper, you can also dye it to a Gun Blue or case-hardened color. Be sure to wipe off any oil or dirt before use. If it accidentally gets into a wound or mucous membrane, rinse immediately with clean water. Processing method: Room temperature immersion, brush application, spray, etc. Dilution ratio: 1 part concentrate to 7 parts water (8x) For application, 1 part concentrate to 3 parts water (4x) The processing technique is extremely simple. Even if the workpiece has a complex shape, a uniform film can be created. Since the processing temperature is room temperature, it does not damage the material. It is odorless and non-flammable, and does not deteriorate even with long-term storage. There is almost no change in dimensions before and after processing. Blackening, rust prevention, CAROMSHOT, Carom Shot, HWS, Hartford, G.Smith.S, G. Smith.S, Indi, Indian, BIRCHWOOD, Aluminum Black, Tobika, Blacky