John Robertson wrote in news:nuCdnRjVXeEzW snipped-for-privacy@giganews.com:
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Far better solution for *this* application. Have a presice mask made from say PCB solder paste stencil media.
IOW have a stncil made that has openings for the LEDs.
Send that off to the UK's "National Physical Laboratory" to get coated with "VANTABlack" coating. Apply to PCB assembly. There is no blacker surface treatment.
"How much more black could it be?"
"None more black."