How to formulate a Pewter Patina

We are new to the manufacture of pewter counter tops...we have achieved polished and linished finishes but would like to create a gun metal grey coloured patina that has a uniform finish. We would prefer to be able to blend our on solution. Can you advise.

Home brew can sometimes be cheaper, but you have zero tech services help when the solution does not work quite right.

I would use a proprietary until you get some experience with it.

Try immersion in 20% iron(III) chloride solution.Dark grey to black finish. Objects must be grease and oxide free.Hope it helps and good luck!

At internet archive website you can download old book on metal coloring by Arthur Hiorns-old but very good book with chapter on coloring of tin and pewter.
Hope it helps and good luck!