Improving my rust blueing of guns

I am trying to perfect a rust blue using the usual copper, acid, salts, etc everything is going great except the colour needs to be a deeper ebony black I have tried a higher copper content but it just seems to stop the solution making the metal rust any suggestions?

"Firearm Blueing & Browning"
by R. H. Angier

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You need to heat the bluing mixture to 50 °C this should make the copper combine with the barrels and in turn giving a blacker tougher finish. It sounds crazy but 15 years of restoration I can assure you this is the best way.

I have been there.

Thanks John I will try this, since my last message my work has improved greatly, so this will be an added bonus, I had trouble with the water so started using rain water, this has also helped but I keep getting the odd grey patch at the top or bottom end of the barrels. I know I have been thorough with degreasing etc?