Problem in making antique brass

Hello every body...
I am facing problem while I convert plated brass to antique brass...to make antique I had use a mixture of sulfuric acid with copper sulphate ⇦ on eBay or Amazon [affil link] and silinium oxide this solutin make brass black-brown color then the article run with soap in stones...

now my solution not convert brass to black- brown color it make black spots on article and the entire object become damage

can any body have solution of this ?
any other composition is more effective to make brass antique?

Uroj,
You have become a product development chemist. You are trying to recreate what others have already done in the realm of proprietary chemistry. Those people have also investigated the reasons for problems using their processes. They know which are from the process and which are due to plating, etc. This is why many people buy proprietary processes - you are not just paying for the chemicals but for the technical expertise of the suppliers employees.

Uroj
Gene is quite right for most processes but brown/black is very simple chemistry.
Just about any soluble sulfide will give this colour on brass.