Gun Blue

This is a simple recipe, the chemicals needed are easy to obtain and relatively cheap. Using a few precautions a professional finish on par with the best gunsmiths can be obtained.

Warning: This is a hazardous process. KnifeKnowHow.com takes no responsibility for any harm that befalls the person who attempts this. Read and reread these instructions, make sure that you understand them.

Hardware:

A stainless steel tank, large enough to hold the parts to be blued. The depth of the tank should be at least three times as deep as the amount of solution it will hold. This is to prevent splashing of the chemicals.
A steel or plastic container of the same size.
A gas burner or two, large enough to heat the entire bottom surface of the stainless steel tank.
Thin wire to suspend the parts in the solutions.
Rubber gloves.
Some stainless steel wire (1.6mm 308 TIG wire works well)

Chemicals:

	Degreasing liquid or strong dishwashing liquid
	Acetone, alcohol or MEK
	Caustic Soda (NaOH) pellets
	Ammonium Nitrate (NH₃NO₃)
	Table salt (NaCl)
	Linseed or soluble oil
	Gun oil, tool oil, WD40 or similar

Step one: Polishing and cleaning the components to be blued:

The first thing to know about bluing is that it will not cover any scratches. The finish applied will directly influence the result. A mirror finish will give you a gloss bluing job, a satin finish will render a matt blue.

Next you must thoroughly degrease the part. This includes removing all fingerprints and the reason why you must wear rubber gloves. (put on the gloves and wash them with degreaser to get rid of any oils on the outside of the gloves)
Wash the parts with degreaser and rinse under a strong stream of water, attach the wire hooks, and suspend them in a bowl of boiling water.

Step Two: Preparing the solutions:

Warning: Follow these instructions carefully, in exactly the order given else disaster may result!

Dissolve 0.5 kg caustic soda in 1 liter water (Any drinkable water is fine.) and bring to a boil.

Warning: This solution comes to a boil quite abruptly and can “erupt”, splattering you and the surrounding area with hot caustic soda.. Stand well back and wait for it to come to boiling heat.
Warning: Hot caustic soda is just as dangerous as any acid. Wear eye and face protection, as well as an apron and old clothes. If it does splatter on your bare skin, wash with plenty of cold water.
As soon as the first “eruption” takes place, turn down the heat so the solution is steadily boiling.
If you have a extraction fan, now is the time to turn it on.

Step 2:

Carefully, very very carefully and slowly add 0.25kg Ammonium nitrate. (It is best to add small amounts at a time until you have added the whole lot.)
Warning: Adding the Ammonium nitrate to the caustic soda solution will release a considerable amount of ammonia gas! Get upwind until the gas dissipates before adding some more.

Add about a tablespoon full of table salt to the mixture and bring to a steady rolling boil.

Step 3: Bluing the parts

With the bluing solution at a steady boil, take the parts from the boiling water and suspend them in the solution. Keep the solution at boiling heat.

Wait about half an hour before checking the parts. When the colour is to your satisfaction, transfer to the oil and leave for half an hour.

Remove the parts from the oil and hang to drip dry and cure for at least twenty four hours. Do not touch the parts during this period.

Wash the parts by washing in warm water, then re-oil with a suitable oil such as is used on guns. Q20, 3 in 1, or WD40 will also work.

When the bluing solution is cold you can store it in a glass or plastic container and keep it for the next job. (It save you the effort of going through this whole dangerous process from the start.)

Failures:

These are the result of either oil or grease on the parts or too much water in the solution. It may also be that the solution has become weakened due to being re-used too many times. To replenish the solution, add a table spoon or two of ammonium nitrate to the solution when it is at boiling heat. (Ammonia gas will be liberated during this process).

You will note that harder steels gives a different colour in relation to softer steels. This may range from a straw yellow, to gold or even a red colour.

This solution will dissolve all tin and lead based solders, as well as solders that contain a large amount of zinc.

About Ammonium Nitrate:

Ammonium nitrate is a commercial explosive. It is also used as a garden fertilizer, with limestone added to render it safe. (LAN = Limestone Ammonium Nitrate). Ask your local nursery or garden supplies for a bag of LAN. Check the bag to make sure that there are no other additives such as phosphates or bone meal. You can use the LAN as is, or dissolve it in water and leave for a day or two. The limestone will form a sediment on the bottom, and you can then pour the clean solution out. The amount of water in the bluing solution will affect the effectiveness of the bluing process, so if you decide to dissolve the fertilizer first, be sure to use less water when dissolving the caustic soda. You can also use some of this solution to replenish the bluing solution. (Remember that ammonia gas will be liberated.)

To mix larger volumes: The ration given above works for any volume of solution.

5 liters water	2.5 liter water
2.5kg Caustic soda	1.25 kg Caustic soda
1.25 kg LAN	0.625 kg LAN

Remember that the container for the solution should be at least three times as deep as the level of the solution in the container to prevent splatter. (For five liters of solution you would want to use a fifteen liter container.)