'Dullify' shiny zips

[lurkingaround]

I've already posted this in Style and Beauty, so apols if you're reading again.
I have boots with very shiny brassy zips that I don't like much. I reckon I would wear the boots a lot more if I could lessen the shine.

Is there any way to do this? TIA.

www.kernowcraft.com/products/metal-clay/liver-of-sulphur-C172/

Do consider that you could ruin the boots as this looks quite tricky to me.

Thanks Sunday! I wonder would it ruin the boots. I could use a tiny paintbrush. Might give it a go on something very old and waiting to be dropped to charity. Thanks again!