As discussed in the article What Blue Solution to Use I explain that it does not really matter what you use as long as it is corrosive, in the article I compare salt water with rust blue solution and end up with the same result.

However I still get people contacting me asking what solution I use as the one they use doesn't work. My advice to everyone on the topic is keep your solution simple. I have had people contact me because their firearm is turning an odd colour, when I ask what is in their rust blue solution, the number of ingredients is as long as your weekly grocery list.

Further advice to people is, if they are only going to do a single firearm or two, just use salt water. It is cheap, non toxic and does the job well. If you are going to be doing a lot of firearms, then yes, making your own solution is a good option.

Above is a picture of the chemicals and equipment you are going to need, they are listed below in roughly left to right order from above:

• A glass container for storing your solution - I use a 500ml amber bottle
• A small scale
• Iron Filings
• A volume measure
• Nitric Acid - I use 70% concentration
• A funnel
• Distilled water
• Hydrochloric Acid - I use 320g/L concentration
• A glass jar
• Gloves
• Eye protection

Note: While not shown it is recommended that a respirator be used.

The funnel, glass jar, gloves, eye protection, distilled water and the scale should all be easy to find. The rest as below:

• Iron Filings - I purchased some off ebay, but I have also run a magnet on the floor of my workshop and collected a heap of what is filed steel, which is mostly iron. There was no noticeable difference between the two sources. 
• Hydrochloric Acid - Readily available at hardware stores, the concentration I use is simply what is stocked by my local store.
• Nitric Acid, Glass Container and Volume Measure -  All of these were available to me from a local chemical supply store usually catering to schools for educational purposes.

The method of mixing these ingredients is fairly dangerous. The act of adding the iron to the acids produces a huge amount of gas, which if your not careful could overcome you. I mix the ingredients outside on a glass top table. Below are the steps to mix the ingredients to fill a 500ml bottle:

1. Pour 420ml of distilled water into the amber bottle
2. Using the volume measure, pour 29ml of hydrochloric acid and 35ml of nitric acid into the jar
3. Using the scale, measure out 13.3g of iron filings
4. This is the most dangerous part of the process, slowly add a small amount of the iron filings to the jar with the acids in it. The process of adding the iron to the acids creates a very aggressive reaction, it often starts off slow and then woosh! takes off. It is not explosive, but similar to opening a bottle of beer you have shaken. For this reason I put the jar in an old pot to catch any overflow. See image below. The danger comes mostly from the amount of gas created, so stay well clear after adding the iron. 
5. After the iron/acid reaction has finished, you will be left with what looks like a disgusting mess of frothy sewage (it doesn't smell like sewage, but does have a unique smell). Pour this frothy sewage into the distilled water in the amber bottle using the funnel. Note the frothy sewage water will have iron filings still in it, I do not strain these out, I just tip them straight into the amber bottle.
6. The jar will most likely have a lot of the froth stuck in it, I usually tip a small amount of fresh hydrochloric acid into the jar, put the lid on and swish it around to collect the last of the frothy goodness. I then tip this into the amber bottle.
7. You now have rust bluing solution. This solution will usually last me at least a dozen long arms.