Need mordant wash for galvanized steel

For a museum exhibition, I need to replicate / match the surface treatment applied to corrugated galvanized steel sheets. The original work was done in the UK using a product called "T Wash" sold by a company named Decorating Direct, intended as a paint pre-treatment to be brush applied after degreasing and detergent washing.The resulting 'look' is a mottled darkened 'patina' with white streaks.

I can't find an ingredients list for this particular product, but a MSDS for a similar proprietary solution lists 2-BUTOXYETHANOL, PHOSPHORIC ACID, and PROPAN-2-OL.

This type of consumer product seems to be common in the EU countries, but due to a short deadline, I would like to find an equivalent locally.

If galvanized=zinc plated you can try 2heaping teaspoons salt/1 teaspoon copper sulphate ⇦ on eBay or Amazon [affil link] /1 cup water solution(dark gray to black finish). Hope it helps and good luck.