Availability of hydrofluoric (HF) based glass etchant

[dogzbum]

In Australia HF based products for glass etching have been banned since 2003 because of (damn) graffiti taggers using them to deface shop windows. So glass etching products are no longer available to the retail market.

After some disatisfaction with the quality of the ground glass I was making via the valve grinding paste method I decided to do some investigation into other sources of HF products.
Some Googling revealed that HF is primarily used in the metal fabrication industry for removing oxides on aluminium and stainless steel. These 'pickling pastes' are readily available at welding supply stores however not in small quantities and not cheaply (4L for AUD$65).
Further Googling revealed a less expensive and easily available product which contains 9.8g/L HF and 38g/L H2SO4, making it ideal for glass etching.

SEPTONE (www.septone.com.au) 'Ali-Brite Aluminium Cleaner' is available in a 1L bottle for AUD$11.99 at Super Cheap Auto stores. Apparently it is also widely stocked at boating and marine retailers.
I am sure there would be a similar product available to overseas buyers - check your local marine or auto shops for aluminium cleaners (or aluminum for those unfortunates who cannot afford to waste an extra 'i').

Before you rush out to buy some please read the MSDS (http://www.septone.com.au/msds/ATA1.htm) as this is one of the most toxic, corrosive and plainly dangerous chemicals that you could have at your house. Make sure you use all the personal protective equipment (PPE) specified and that you are suitably qualified or confident to handle toxic and corrosive chemicals.

Last night I cracked a bottle open (wearing appropriate PPE) and sat some 3mm glass in undiluted Ali-Brite for an hour. The glass had been etched to about 2mm where it was submerged. This product is very effective at etching glass and from now on I will use it to make ground glass for my cameras. To pattern the glass I am considering using plain candle wax as a mask, from memory this is resistant to hydrofluoric and sulphuric acids. (Please let me know if this is not true or if there are better materials).

Notes: 1. I have no affiliation with any of the companies mentioned, I am merely passing the information on for others wanting to chemically etch glass. 2. Do not even think about using this stuff if you are not willing to take adequate precautions, I don't want to read about your death or amputation of your limbs due to HF accidents.

 

[Photo Engineer]

Just as a side note, all products produced by reaction of human flesh and bone with HF are volatile gases. Therefore, it etches skin and bone rapidly due to the gases boiling away from the surface of the wound.

This is one of the most terrible, corrosive and toxic compounds that you can use. Please use it with caution. It can produce a huge burn in a very short time.

PE

 

[richard ide]

Hi
I think a couple of better products for masking would be: 1- beeswax as it will stick a lot better than the paraffin wax. 2- enamel paint, just wash it off with solvent after etching. Lee Valley Tools sell a glass etching cream.

 

[Murray@uptowngallery]

If I read Mr. Dog's description unhurriedly, it sounds like it etches deeper into the glass than I would have expected...like I think I need to re-read the description.

I would hope for a uniform etch that doesn't significantly alter the glass dimensions.

I still like my 500-600 grit blend dry Silicon Carbide. On smaller pieces I mix random amounts of 600 SiC and 1000-1200 aluminum oxide. It's a little bit of work, but I can control the results.

On big ones (biggest I've done was 16x20..might be bigger, I forget, still in the garage for a 'someday' project), the grit blend takes too long. If I did it again, I'd stick with the straight stuff.

I got the SiC from a lapidary supply guy (rock polishing). I got the aluminum oxide as a sample from some abrasive company...I forget who...they sent me a 1# tub.

Murray

 

[Struan Gray]

I love this bit:

"In these cases, the necrotic tissue should be excised and the gel massaged into the base of the burn, taking usual aseptic precautions."

I can just see the kids crowding round to watch as mom wields the kitchen knife.

I use HF pretty extensively for preparing and processing semiconductors. I teach undergraduate and postgraduate students how to use it safely. I wouldn't have it anywhere near my home, and I wouldn't trust the average DIY-ing photographer to come within a mile of it.

I am not trying to be alarmist, but HF burns are not like other acid burns: even at low doses they have the potential to cause a pain that is intense, incurable and persistent. I recommend that people think really hard and long before using it in a hobby context, even if it is available cheaply at an auto parts store.

This is not a crack at you Dogzbum, but rather a heads up to the tinkerers. From my experience with students I know that HF is underestimated because people think it is just another strong acid. It isn't.

 

[Murray@uptowngallery]

I don't even know if you can get an even etch with HF: wouldn't it depend on applying an even layer, and how would one measure that?

Dave at Satin Snow takes care to maintain some degree (I don't know the quality control process) of maintaining a flat product in the end (starting with specified flatness on the raw glass).

I didn't think/know variation in the flatness of the groundglass imaging surface was critical, but there is some web chatter about this.

I haven't worried about it much; most of my camera-building projects get to the image-on-ground glass stage only & I start another, or any focus problem is far outweighed by an exposure error or my krappy komposition skills. (YMMV).

Say, Struan, isn't HF considered a 'weak' acid (only a single H, as far as pH goes, but very active due to the Fluoride...high electron affinity or sumthin')? I shouldn't profess to remember much chemistry, but I remember HF and H3PO4 (notable for 3 hydrogens in cola beverages and rust removers) were pointed out as unusual entities in the pH (power of hydrogen) category.

Murray

 

[Struan Gray]

1mm removal in an hour is a lot more agressive than the hobby glass kits will manage, but the MSDS says Septone can have up to 10% of HF, which is a fair bit. Also, the glass was in continual contact with a large reservoir of gel, unlike the case if you smear a thin layer onto a glass panel. The HF molecule is so small and so light it diffuses fast over long disances - one of the reasons it is so nasty when it hits the body.

Wikipedia's article on hydrofluoric acid seems measured and correct, and mentions the difference between highly corrosive behaviour and low pH.

http://en.wikipedia.org/wiki/Hydrofluoric_acid

The linked article on car washes describes a similar situation to hobby photographers using HF to make their own ground glass: the results don't really seem worth the risks.

People here are grown ups (mostly) and can make up their own minds, but for me, using HF is up there with mercury intensification as a game not worth the candle.

 

[Photo Engineer]

Murray;

HF is a strong acid by virtue of the fact that you get nearly 100% disassociation into H and F ions. That is what makes it strong. Acetic acid is weak because there is much less dissacociation and you get few H and OAC ions. It is mostly HOAC in water. OTOH, HCl is H and Cl in water and is therefore a strong acid and H2SO4 can be H and HSO4 or H, H and SO4 or any mixture in between. (HOAC and OAC are chemists abbreviations for acetic acid and acetate ion)

I have not put the charges in as it would be confusing.

PE

 

[Jim Jones]

. . . To pattern the glass I am considering using plain candle wax as a mask, from memory this is resistant to hydrofluoric and sulphuric acids. (Please let me know if this is not true or if there are better materials). . . .

For putting a grid on a ground glass I scribe the lines in the ground side with something that breaks down the roughness of the ground surface to leave a thin and somewhat bright line. This is less obtrusive than any line that can be painted on with resist or perhaps drawn with paint or pencil. A ball point pen that no longer deposits ink often works well for scribing.

 

[Roger Hicks]

...for me, using HF is up there with mercury intensification as a game not worth the candle.

Dear Struan,

The perfect analysis. I'm sure it works; I'd be confident I could take adequate precautions; and I'd still consider it more trouble than it's worth.

Cheers,

Roger

 

[Neanderman]

HF is a strong acid by virtue of the fact that you get nearly 100% disassociation into H and F ions... etc.

I have not put the charges in as it would be confusing.

Even without the charges, a clear and lucid explanation for people without a lot of chemical knowledge.

Thanks.

Ed

 

[Murray@uptowngallery]

Thanks, PE, et al. (letters I can probably use correctly).

Murray

 

[freygr]

HF acid, Is just too dangerous. Heck in less than a hour with 600 grid, water, and using 4x5 and 2x3 glass tools, I had a 11 by 14 inch piece of ground glass form float window glass.

 

[Ole]

There's yet another way...

Calcium fluoride, CaF2, is insoluble. Yet a fine powder in contact with glass will dissociate enough in strong hydrochloric acid to etch the glass.

I discovered this when cleaning calcite off an otherwise nice mineral sample with quartz and fluorite - the calcite disappeared as it should, but the quartz was etched too. I hadn't seen the frosting of fluorite...

 

[Struan Gray]

Ole, are you sure you didn't just dissolve the flourite? That's how they make HF industrially.

 

[Ole]

Struan, the (formerly) nice bright shiny top of the quartz crystal was definitely etched. Some small fluorite crystals which had been embedded in the quartz were now sitting on top of little "humps" of quartz.

 

[Struan Gray]

Sorry Ole, I just had a brainfart and forgot that fluorite *is* CaF2.

I'll go and get that second cup of coffee now....

 

[grahamp]

I used to use HF to dissolve silicate rocks for analysis as well as etch them for certain processes. For etching we used to use a plastic dish with the HF (very little) and suspend the object for etching over it and let the vapour do the job. The surface had to be grease-free, including fingerprints. Dunking the sample generated too much local gas pressure and disturbed the crystals on the surface.

All this was in an acid-rated washable fume cupboard, with neutralizing solution, barrier gel, double gloves, face masks, and lots of calcium glauconate on hand. It was also an organic-free lab. The local hospital had an advisory that we used it.

The geologists used to scare the chemists with this stuff. Even 'cut' to 10% or so I would be very cautious.

 

[Bandicoot]

I'm familiar with HF, know the precautions and so forth. And I wouldn't use it, absolutely not. Not worth the risk.

YMMV, but something that could kill me or cause intense and irreversible pain is just not something I need to get involved with for the sake of a focusing screen. Especially when granite surface plates and diamond grinding powder are so (relatively) cheap these days.

However, if etched rather than ground glass is an absolute essential, anyone have thoughts on using warm phosphoric acid? That strikes me as a safer (safer, not 'safe') alternative to hydroflouric acid, and more controlable too.


Peter

 

[dogzbum]

To clarify a few of the responses:

• Yes, I agree this stuff is deadly, dangerous and unpleasant. Take all precautions if you decide to use it.
• No, I do not agree that it is too much trouble to bother with. A chemically etched ground glass is 2 to 3 stops brighter than surfaces produced using the 600 grit abrasive method. If you're doing medium or small large format work (apologies for oxymoron but 5x7" or less is tiny) this can be a real advantage for focussing.
• Yes, diluting the mix about 1:10 with H2O will give a slower more controlled etch.
• No, You will never get dead flat surface when etching glass but this is because glass is amorphous, not crystalline. Note however that IMHO the etchant gives a smoother finish than the abrasive method and I assume this is because you are removing material from the total surface area rather than breaking chunks off where they stick up.

My intent was to make this useful technique available again to others who were not able to easily source a chemical glass etchant. I acknowledge that the technique is VERY dangerous and uses toxic chemistry.

For me personally the benefit of a 2 or 3 stop brighter viewing screen offsets the risk involved as I am happy and able to use the appropriate safety measures.

I would never store this in my own household and recommend that you do not either. I would much prefer to leave it at work (yep! in the tea room :munch: ) or dispose of the remainder when I'm finished. It's cheap enough to throw away and buy another if you need to.

Etching gives a much smoother finish and appears to produce a flatter surface than the abrasive method.
I have not personally measured the surface roughness / flatness of samples but the etched surface seems flatter and smoother.

Also, since the initial post I have found that etching an already abraded surface (I generally use valve grinding paste) gives the best result as unabraded glass tends to remain too transparent (or do I mean clear?) for good viewing or focussing. This goes back to my assertion that the surface is flatter / smoother than the abrasive method: If you etch a clear piece of glass it remains clear, so it seems the entire surface is being etched evenly.

Thanks also to Richard Ide for the response recommending alternative masking materials. When I get some more glass I'll probably give beeswax a go as a mask. I suspect the high sulphuric acid content might eat enamel paint.

 

[Mustafa Umut Sarac]

If I am not wrong , the problem is to create a bright focusing screen.
At first at minolta than at Hasselblad , they used plastic screens which crafted with mixing polymer and transparent fibers. Transparent fibers created a internal surface for focusing.
Why you are not creating focusing screens from acrylic , polyester or clear epoxy ?
May be an idea but worth to study.
I will look to the patents and write again

Best ,

Mustafa Umut Sarac

 

[DaveOttawa]

Dear Struan,

The perfect analysis. I'm sure it works; I'd be confident I could take adequate precautions; and I'd still consider it more trouble than it's worth.

Cheers,

Roger

FWIW I concur, and yes I have personally used HF based reagents in both semicon & metal finishing environments. It was only just worth the trouble in a professional, "I was getting paid for it and had a full rubber suit etc etc and a safety drench shower and gluconate first aid kit and panic buton within reach" environment.
Also FWIW it's weak acid not a strong, acid using those terms in the chemical jargon not colloquial sense. But that isn't important to the OP's practical application, HF is unusually hazardous.