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How can I etch dichroic glass?

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GreySoul

Wed Mar 21 2007, 04:04AM

Registered Member #546 Joined: Fri Feb 23 2007, 11:43PM
Location: Albuquerque, NM
Posts: 239

Ti or TiO2 - good question I will call the manufacturer tomarrow and find out. they think I am crazy for wanting to etch perfectly good dichro coated glass. - silly lab scientists. FWIW the coating process is done in a high temperature evacuated chamber to prevent oxides and assit in even coating - so I suspect I'm not dealing with an oxide here - but I could be very wrong.

the glass transmits cyan and reflects yellow if that helps any.

As for acids, I've never had a problem dealing with fuming nitric, but I know HF is much nastier stuff. I'd keep it tripled up in poly bottles and jars at the very least.

Problem is my nitric supplier (jewelry supplier) doesnt have HF.

Is there a basic sythesis I can do to get a decent strength HF solution?

-Doug

Eric

Wed Mar 21 2007, 06:35AM

Registered Member #69 Joined: Thu Feb 09 2006, 07:42AM
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Posts: 116

Ammonium biflouride is used for etching glass, I imagine this would work. It is a safer alternative to straight HF and is also alot easier to obtain. Of course it will etch the underlying glass too so you'd have to stop the process once the dichroic coating was gone.

Bored Chemist

Wed Mar 21 2007, 07:06AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

Metals ( give or take copper gold etc) reflect light whatever the wavelength and so wouldn't help much for a dichroic filter.
TiO2 has a high refractive index, SiO2 a relatively low one. Those are what you need for assembling dielectric structures as filters, reflectors etc.
It might be easier (if you are on good terms with the maker, to put a resist pattern on the glass before coating it.

ragnar

Wed Mar 21 2007, 10:17AM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
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You can purchase adhesive dichroic films for application to existing windows -- I suspect it would be easy to cut these up (with a CNC plotter, lasercutter, etc) and to then apply the stencil onto regular glass...?

Chris

Thu Mar 22 2007, 12:09AM

Registered Member #8 Joined: Thu Feb 02 2006, 04:34AM
Location: Harlowton, MT, United States
Posts: 214

Is there a basic sythesis I can do to get a decent strength HF solution?

You can obtain it by thermal decomposition fluorocarbons such as R-134a refridgerant (1,1,1,2 tetrafluoroethylene) at 500C with air and steam. The HF can be condensed out after decomposition, but this all has to happen in a passivated nickel or platinum group metal plated aparattus. One of the intermittent products is fluorophosgene, which is a VERY deadly gas. The final product could be anywhere from nearly anhydrous HF (also very deadly toxic, and volatile) to very dilute solution depending on how much water you inject.

You can also obtain HF by the addition of concentrated sulfuric acid to fluoride salts. Again it will need distilled out as anhydrous HF, and require similar aparattus. Given the complexity, expense and possible dangers of either process, I can't imagine doing it unless you really need HF often and can't obtain it. It's really nasty stuff.

I would rather use a fluoride electro-etch process on titanium than hydrofluoric acid based etchants.

Metals ( give or take copper gold etc) reflect light whatever the wavelength and so wouldn't help much for a dichroic filter.

Very thin layers of metal are not neccessarily opaque. You are implying that even a layer a single atom thick of metal will be totally reflective and opaque to all forms of electromagnetic radiation. Many "colorless" materials, when in a thin layer, tend to transmit more red light while reflecting blue. Try it with a sheet of virgin grade teflon or polyethylene.

Dr. Shark

Fri Mar 23 2007, 11:45AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

As BC pointed out the coating would most likely be TiO2, a metallic coating would not make sense for this application.
I have a gut feeling that both quartz and TiO are a lot more resistant to etching that the glass substrate, meaning that you would mess up the glass if you etched through the coating. Grinding a hard coating off a soft substrate would leave you with the same problem.
Are you sure there is no other way for your application?

GreySoul

Fri Mar 23 2007, 03:01PM

Registered Member #546 Joined: Fri Feb 23 2007, 11:43PM
Location: Albuquerque, NM
Posts: 239

(in my best space villian voice)

I could use zee freeekin' laser beam.

no but really... I don't have a "freeekin' laser beam" capable of this.

The "dichro slide" and other applique methods are either prohibatively expensive or would burn off under the heat these tiles will be exsposed to.

I could contact the manufacturer to make a custom mask when the glass is coated but a custom set up is $$$$.

I've been told by some fellow glass workers that ammonium biflouride paste will actually work, it just takes a while and has to be washed off before it gets to the boro underneath - I think I'll try that method today.

I will let you know how it goes

-Doug

Bored Chemist

Sat Mar 24 2007, 11:11AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

"Very thin layers of metal are not neccessarily opaque. You are implying that even a layer a single atom thick of metal will be totally reflective and opaque to all forms of electromagnetic radiation. "
Nope, I know perfectly well that you can see through gold leaf. What I'm saying is that you don't get wavelength discrimination from metals in the way that you can get from interference effects using different thicknesses of layers.

GreySoul

Sat Mar 24 2007, 03:13PM

Registered Member #546 Joined: Fri Feb 23 2007, 11:43PM
Location: Albuquerque, NM
Posts: 239

update:

Ammonium biflouride and sulphuric acid = death to dichroic layer and nothing to the underlying glass. SUCCESS!

there is a commercially made solution called "Etch bath" for doing this, but it was hard to track some down locally. Finally got some.

the dichro I am using is, according to the manufacturer, 14 alternating layers of SiO2 and TiO2 for a total thickness of 32nm

The whole idea of dichroic glass is to form an interference layer that will refelct certain wavelengths (in this case yellow) and transmit another color (greenish blue, not really cyan but close)

they accomplish this by putting on 1-2nm thick layers of metal then varying the thickness of the quartz layer and adding another later of metal.

in effect they're making an optical bandpass filter.

google CBS dichro for more info.

Anyways thank you all for your help, putting me on the Ammonium biflouride track was the key, so big thanks to Eric, i owe ya one :)

mods feel free to close the thread if you must - or let it trickle to the back pages in peace :)

-Doug

ragnar

Sun Mar 25 2007, 02:38PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
Location:
Posts: 1425

I'm hoping you'll post some pics or artwork to the thread in due course, before it's closed =D

You've got us all excited now! Hehe

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