I have done a bit of bluing, The cold blues you can buy are quick & ok for small screws etc but are not durable. The other methods are a hot caustic process that is usually used for mass production of firearms & air rifles. Then there is slow rust blueing which is a high quality process. The steel is polished & prepped, degreased & the rusting solution applied, There are literally hundreds of recipies often containing poisonous substances like mercury chloride, ferric chloride etc. It is left for a while until it has a uniform coating of rust, the loose rust is then carded off with a soft iron brush, then you repeat until a deep brown is achieved. If you boil the part between passes the iron oxide is changed from ferrous to ferric oxide which gives the blue colour.
Process can be done at room temperature & can take up to 5 or 6 passes until depth of colour is achieved.
Many older damascus barreled guns were browned as this shows the figure in the barrel better than bluing.
The book Fiream Bluing & Browning by RH Angier is worth reading & gives chapter & verse.
It isnt a good idea to have bluing tanks in a workshop full of good machines unless you want them to go rusty!
Process can be done at room temperature & can take up to 5 or 6 passes until depth of colour is achieved.
Many older damascus barreled guns were browned as this shows the figure in the barrel better than bluing.
The book Fiream Bluing & Browning by RH Angier is worth reading & gives chapter & verse.
It isnt a good idea to have bluing tanks in a workshop full of good machines unless you want them to go rusty!
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And I'll not be buying to try, my name doesn't contain the words 'Sultan' or 'Brunei' 
