Copy Cad Zinc Blackener

[Homba]

This is my first post on the forums, so Hi to you all.

I'm having difficulty achieving a black finish on a zinc workpiece. It was previously phosphated, and I have stripped it back to the metal using Birchwood Casey Blue and Rust Remover (Sulphuric and Phosphoric acid based), and steel wool. I have previously treid using Birchwood Casey Aluminium Black, which does impart a truly black finish to it, but often turned out patchy, as you do not get enough solution in the bottle to immerse the part. So I bought Copy Cad Zinc Blackener, and following the instructions, made a 10% solution. I thoroughly scrubbed the part using the Blue and Rust remover and steel wool, and then rinsed it thoroughly and placed it into the Copy Cad solution for 5 minutes, agitating the part. I then removed it and rinsed it throughly, and left it overnight. I even tried degreasing it after rinsing it - the finish I get using this method is only a dark brown, even when I seal it using WD40 - what am I doing wrong? I'm convinced that I would get a nice deep black if I sandblasted the part with aluminium oxide grit, but I don't have acess to a gritblaster of any kind. Can anyone recommend a better way of pre-treating the metal to get a better finish please?

Your help will be very much appreciated.

Gary

[Homba]

I have tried to blacken this piece 8 times, thoroughly stripping it back to the shiny metal each time beforehand, but still it only turns out brown, and now I have used up all the concentrate.

I have since noticed from other posts on this forum that the instructions are wrong, and that I should be mixing the solution 1 to 4. The container I have says 'Copy Cad & Zinc Blackener New Formula' and the label advises to mix 1 part to 9 parts of distilled water. Since I live in the UK I bought it from Caswell Europe - would they be willing to provide me with a replacement container of concentrate?

[seanc]

I don't use the blackener on anything but pure plated parts, so this may not eb entirely applicable, but ...

I'm having difficulty achieving a black finish on a zinc workpiece.

What is your "zinc workpiece"? pure zinc or a die-cast alloy? The blackener needs a high percentage of zinc content.

It was previously phosphated, and I have stripped it back to the metal using Birchwood Casey Blue and Rust Remover (Sulphuric and Phosphoric acid based), and steel wool.

I'm not familiar w/the Birchwood products, but if it's got phosphoric acid, you may be re-phosphating the part, preventing the blackener from reacting with the zinc.

Why not use just 5% sulphuric as recommended in the manual?

Can anyone recommend a better way of pre-treating the metal to get a better finish please?

I think you need to better identify the metal alloy. If it doesn't have high zinc content, it just won't work as expected.

Sean

[Homba]

Hi.

Thanks for your reply. The workpiece I have is a die-cast zinc-alloy (95% zinc). When I apply the acid stripper, It phosphatest he surface to a dull grey. I then vigorously remove the phosphating by scrubbing with coarse steel wool back to bright zinc. Here is the MSDS for the stripper that I am using. http://www.birchwoodcasey.com/sport/.../16125-BR1.pdf

I cannot use sulphuric alone as it unfortunately isn't available here in the UK.

[KCV6]

Sulphuric should be available as 33% from your local car battery supplier. just mix 30 to 60 mill per litre of water to get bright dip.

[Homba]

I'll see what I can do. You used to be able to buy it from these places but they stopped it a long time ago due to people misusing the acid.

[KCV6]

Yep, I understand, much the same here, I had to explain what I use it for, kinda helped that I had my work ID on at the time. Possibly try a chemical supplies place and ask for 10% sulphuric in a 5 litre container or 20 litre cube. Far less likely to ask questions then.

Cheers

Mark