Phospate for satin finish grey on low carbon steel?

[alexit]

Customer has asked that we change from clear zinc finish to a satin-finish with uniform grey appearance. This is a welded lever arm that cannot be painted so I search for new process. I like the gloss finish black from salt-nitride or waxed black-oxide myself but customer is always right.

From my searching, both zinc and manganese phosphate coatings can produce components with grayish velvet finish. I ask:

Is this process going to be uniform at 1000 pcs per batch, 5-10 batch per year? How should I specify this to achive desired neutral reflectivity (% compounds, time in bath, etc.?)

Any other process can be done cheaply in PRC or ROC to get desired conversion-type finish?

Thanks,
Alex