Best Environmental Protective Coating Over Silver

Normally you shouldn't put a coating over a coating that has no adequate adhesion onto the layer.

The new coating will ruin the first one. Did you consider electrolytic coating - Gold and Platinum are the toppers and need no further protection.

Yes, thanks, I nickle plated an ABS box as an alternative (stronger, but still investigating properties). Apparently one cannot electroplate onto FRP (Fibre reineforced plastic).

I agree the base coat to surface is more the issue, but was hoping to overcoat with some sort of epoxy paint to prevent scratches caused by handling and installation.

If you've got the capability to vacuum metalize, then the normal top coats should be adequate. From memory GLYPOXAN was used for Al, Ag, Au in a previous location.

Your basecoat adhesion though is of concern. Your vacuum metalizing (equipment) suppliers will be able to recommend a compatible base coat and top coat.

By the way, if the layer is "a few microns" thick, then that's a prety thick vacuum metalise.

If it's only to measure H and not to be optical grade, why not just let it oxidise?

Thanks, it's outsourced, I'll ask them if a topcoat like GLYPOXAN can be used in future, sounds good. Sorry, regarding the thickness-yes it's probably much thinner (thou's mils microns, I'm not used to the scales) anyhow I'll ask them how thick they do/can go, for interest. I wasn't planning to coat, just found it scratches too easily.

Broadband mirrors and those used by astronomers in the optical spectrum typically have a thin coating of SiO to prevent the aluminum from tarnishing. Since aluminum is relatively soft material, the SiO helps protect from scratches as well.

If your assembly can withstand the vacuum of a deposition chamber, you might do well to have them hard coated using a sputtering method and SiO. That your coating is silver rather than aluminum should not make a difference.

To do this properly, however, ideally there should be no outgassing from any of the components

Good luck

Laughing Jaguar

Thanks, yes, Alu would have had a similar issue, please consider this discussion ended

Have decided to go with nickle electroplating onto ABS instead and hope the Nickle coating provides enough UV protection.