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Best black coating for optics edges?

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#1 bigbangbaby

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Posted 08 December 2023 - 01:40 PM

I have an optical window that I want to coat the edges black. I've read India ink works well. What's your experience? Are there better options? Thanks.



#2 AstroApe

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Posted 08 December 2023 - 01:52 PM

I've used black permanent markers to black secondary mirror edges before. It works okay but can leave a shiny reflective coating depending on what type of marker is used, so if you go that route I'd suggest spot testing a small surface and letting it dry to check out the sheen left behind before doing the whole thing.

 

I'm sure there's better options out there but markers are something that's easily acquired (if you're like me there's a desk drawer full of 'em :lol: ) I've never thought about using Indian ink but I think that'd work great. It's pretty dark, and is fairly cheap and easy to get from about any tattoo supplier.


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#3 MeridianStarGazer

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Posted 08 December 2023 - 01:55 PM

The edges of a lens need to be coated with something that gets down into crevices and really makes full contact with the glass, and has a similar index of refraction. Maybe an acrylic base? Nice thing is you can look through the glass to see what test patches get full contact, no air layers. Maybe apply it in a vacuum?
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#4 Inkie

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Posted 08 December 2023 - 02:02 PM

Flat black craft paint, the Plaid variety from WalMart for $3, would do a good job.  You just need a fine brush and a steady hand. 


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#5 rachnoman

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Posted 08 December 2023 - 02:43 PM

Don't need it.



#6 TOMDEY

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Posted 08 December 2023 - 02:54 PM

Absolutely true anecdote > 1970's, at Bausch & Lomb I used a Hydrogen Furnace to blacken (by reduction reaction) lens edges and prism faces. I remember that well because --- I inadvertently exploded the furnace once, when proudly demonstrating it to some OEM customers. I deftly ducked; they all dove to the floor. Nice thing about government programs --- you compile a nice list of frightening anecdotes.    Tom

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#7 bigbangbaby

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Posted 08 December 2023 - 03:09 PM

I'm sure your customers were impressed.


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#8 Oregon-raybender

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Posted 08 December 2023 - 03:16 PM

Shapie Pen does well enough, paints are not the best, been there.

The particles have to be fine enough to get into the ground surface.

Black edge works best in glass that is blacken in special process and

type of glass.

 

Most times it is not needed, the cell works like a baffle. I would guess

you will have window mounted in a cell or mount?

 

Starry Nightswaytogo.gif


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#9 TOMDEY

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Posted 08 December 2023 - 03:54 PM

99% of the benefit is just doing it. The exact material is more on the meh side. That said, I have found that Kodak Opaque (negative film retouching black paint, water soluble) is a great choice because it's optically and chemically benign, doesn't harm coatings, and can be rinsed off with water. I also use Black Sharpie, which comes off easily with 99.9% isopropyl alcohol.   Tom

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#10 bigbangbaby

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Posted 08 December 2023 - 04:00 PM

Shapie Pen does well enough, paints are not the best, been there.

The particles have to be fine enough to get into the ground surface.

Black edge works best in glass that is blacken in special process and

type of glass.

 

Most times it is not needed, the cell works like a baffle. I would guess

you will have window mounted in a cell or mount?

 

Starry Nightswaytogo.gif

Yes, the window is in a cell, its edge resting on 8 cork pads spaced 45 deg apart, so there is a gap between the edge and cell.

 

window_in_cell.JPG
 



#11 TOMDEY

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Posted 08 December 2023 - 04:57 PM

I'm sure your customers were impressed.

When you're ~ladder climbing~ --- nice way to get noticed! Indeed, my nick name was "loose cannon" --- which I swear ultimately led to my serial fellowships. Always wanted to be a serial something or other; mission accomplished.    Tom


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