Effects of using acids on windows?

I am always looking around on people sites to see what they offer for window cleaning. I came across a company that say they use a “restorative solution” which sounded like a water-down acid mix on all first time cleans. I read an article in eClean magazine that said repeated use of acids on windows take off layers of glass; causing distortion over time. my question is if this company is using a water-down acid on windows on all first time cleans should he be sealing them as well.

Good question [MENTION=507]Henry[/MENTION]

It depends on what type of acid you use, phosphoric acid will not harm glass at all unless you’re in an oven at 200C.
Hydrochloric acid will damage the glass if not used correctly.
those are the only acids i have had experience

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I was the guy that wrote that article. I would like to defer to our friend John/Bumblebee who works down in Florida. It is all about the pH. However. There are certain acids that have a very strong effect on glass. There are different visual evidences of these acids. I have developed two different tests which are quite definitive. And have written about them in my blog. The answer to the question about sealants is whenever stains are removed a sealant should be used. However. The wrong acids which I call etchants should NEVER be used. Not even once. I will continue this when I get home from work later tonight. Keep it going guys. The information on this thread could easily save your business.


[B][SIZE=4]Here is a couple of posts from my Glass Smart blog.[/SIZE][/B]

[COLOR=#333333][FONT=Arial][B]This is a test for what I call Total Glass Dissolution. Which is very simply put, the ability of the liquid in question to eat up and dissolve all molecular components of the glass. That would be both the silicas and silicates. In other words the calcium, sodium, oxygen, and silicon atoms.[/B][/FONT][/COLOR]
[COLOR=#333333][FONT=Arial][B]To do this you will first need a small plastic cup. About four inches. Fill it half way with the liquid/product in question. Then take a small/business card size piece of window glass. I use the 3/16 inch glass from a glass shop. You can ask them to cut you some two by three and a half inch (business card size) pieces. They will even smooth the edges so you won’t get cut. Next just drop one gently into your plastic cup half filled with liquid. The liquid should rise about half way up the glass plate. So that half is immersed and half is dry. Let it set at room temperature for about a half hour. Next remove and run it under the tap. Then dry completely. Inspect in bright light.[/B][/FONT][/COLOR]
[COLOR=#333333][FONT=Arial][B]If total dissolution has occurred you will notice a rippled/orange peal like line where the liquid and air met. You might see some clouding above this that won’t go away. The surface of the glass that was immersed should be very clear. You might even be able to feel the rippled line with your fingernail. Probably more on one side of the glass than the other. And if you hold the glass closer to your face and look through it at the distant landscape, then move it a little, you should see the objects viewed through it move a little funny. This line is the site of total dissolution. Of course the surface that was totally immersed was also totally dissolved. But the effect is much more noticeable at this line. Again, if you want to do this test with something that is sure to cause this effect, pick up some sulfuric acid (battery acid) from the auto parts store. But use caution. Gloves and goggles are always best when working with acids. It is a very strong acid. About 37% clear sulfuric.

[/B][/FONT][/COLOR][COLOR=#333333][FONT=Arial][B]So you have bought a liquid wonder product for removing hard water deposits. You have watched the manufacturers video on how to use it. You have read the reviews and talked to other guys about how effective it is. And now you’re ready! Hold on! Please read and do this first. Then every time you hear about another wonder product put it to the test. This first test I discovered by accident. Yet it is one of the most effective and simple tests. No high tech instruments. Just a 3M green pad, some magic tape, a mirror, flashlight, and a very dark room.[/B][/FONT][/COLOR]
[COLOR=#333333][FONT=Arial][B]Take a one by one foot mirror plate. Create a nice patch of scratches in the middle with your green pad. Tape off one side of the patch to keep it dry. Then apply the wonder product to only one half of the patch. Do not let it contact the other side. That is what the tape is for. Give it a good thirty seconds to a minute. Remove with soapy water, and squeegee. Remove tape to reveal the rest of patch. Next take your nice clean, dry mirror into a very dark room. A bathroom without windows works well. Look down the beam of the flashlight at the entire scratch patch. If the product in question has any amount of acid that etches glass you will notice that the scratches that made contact with the product will be very noticeable compared to the scratches that were covered by the tape.[/B][/FONT][/COLOR]
[COLOR=#333333][FONT=Arial][B]I have developed this test using pure acids such as hydrofluoric, sulfuric, and ammonium hydrofluoride. Hydrofluoric worked well for me down to only 1%. If you want to play with a reasl easy to get bad boy you might go to the local auto parts store. Buy some battery acid. This is essentially sufuric acid at a 37% concentration. I got my pint for four bux! You might have to pay up to seven.[/B][/FONT][/COLOR]
[COLOR=#333333][FONT=Arial][B]This test also doubles as a test for crude silicas used in hard water stain removers that are rub on gels, or rubbing powders. It is done the same way. Just substitute the 3M green pad for your product. Rub in your powdered products using a damp sponge. Also rub in your gel without water using a slightly damp 100% cellulose sponge.[/B][/FONT][/COLOR]

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I’m glad your here Henry and thanks again for your time and expertise.

i used some acid yest for 1st time on hard water stainings , neat, and it worked great ! the fumes it gave off were awful so glad i wasnt inside using it.

I have never debated whether it works or not. Many times it works great. Some guys I knew up north used to call it affectionately Hydee. The reason it does work is the same as why it chemically reacts with glass. Both the stains and glass are based on silicates.

Hydrofluoric has a foundness for calcium compounds too. Our bones are based on calcium. So when we get it on our hands it tends to move towards our bones. One guy told me he worked half the day with it using gloves. But it got inside his gloves for the last few hours. When he took the gloves off at the end of the day his skin came off too. Black!

The guys that make crystal glass use a very high concentration of hydrofluoric and sulfuric mixed at a rather high temp to chemically polish their work after it has been polished with a cerium oxide. This works because this type of glass has a high lead content. It is very heavy too for the same reason. The fumes from the vats will travel and etch the inside of the windows leaving them totally white over time. I was called in once many years ago to look at one such problem. The artists was moving and feared his landlord would make him pay for new windows. I can tell you many stories also of guys that did serious damage in the millions of dollars to some world famous buildings. I have been around my friends. I have seen stuff.


Just some more food for thought. Here is an interesting demonstration of what sodium hydroxide can do to soda lime glass at high concentration and high heat. This an alkali not an acid. I think after watching it you won’t be able to argue whether this chem reacts with glass. To understand exactly what IS happening with different acids/alkalies at the surface of glass we will have to get into chemical reactions/equations. This is a real fun video to watch. But please do NOT try to repeat it. Ever.


Just some more food for thought. Here is an interesting demonstration of what sodium hydroxide can do to soda lime glass at high concentration and high heat. This an alkali not an acid. I think after watching it you won’t be able to argue whether this chem reacts with glass. To understand exactly what IS happening with different acids/alkalies at the surface of glass we will have to get into chemical reactions/equations. This is a real fun video to watch. But please do NOT try to repeat it. Ever.


i used hydrocloric acid

Thank-you Henry, for the kind words. As has been mentioned before, different acids will affect glass in different ways. That “frosted,” decorative glass and mirrors you see around, was created using acid.

Yes John. Acids are routinely used for many decorative effects on glass. Glass etching requires a special formula of different acids. When I was a bit more crazy I bought some 100% crystals of ammonium bifluoride. Put them in water. Then hit an old windshield with it. It almost instantly turned a milky white. If the right person knew about this they could waste many thousands of bux in windows in very little time.

And Jonnyald, I remember testing hydrochloric/muriatic acid. It didn’t show any damage to glass. This acid will dissolve concrete. And goes after aluminum quite fast. If the mineral deposits are based on calcium with little to no silicon atoms in the mix then HCL should eat right through the spots without doing any visible harm to the glass. Acetic acid or vinegar is another acid which will not visibly harm glass. Sulfamic acid, or oxalic acid are both organic acids. They also will not do any visible harm to glass. I remember testing phosphoric acid at room temp;…no harm. Although this is listed as a glass etchant at higher temps. Nitric acid will not harm glass either. It also won’t go after aluminum. But does eat up concrete very well. So it would be an interesting choice for taking concrete off glass. It is just somewhat controlled because it can be combined with sulfuric acid and glycerin in just the right way to make nitroglycerin. If you buy it and try you might not make it out of your kitchen if you succeed.

I had several different tests for the acids. The simplest one which was the most fun was to simply sink the metal or powders in question in a cup full of the acid in question. If I got any reaction at all I could see small gas bubbles form and rise like the fizz in a soda/tonic. A real strong reaction gave me lots of fizz. I could even rate the different acids with different metals this way. I even constructed a kind of test tube I could stick on glass for this purpose. Although it was more of a looking glass that stuck like a suction cup which I could fill with any acid I chose. Real low tech stuff that was quite effective at giving me answers. I devised this contraption because I was looking for a way to put the mineral deposits in a test tube and fill with an acid. So rather than scrape them off (which I couldn’t do very well) I created this device. It worked well but didn’t show any gas bubbles. Maybe because the mineral deposits were based mostly on silicates not calcium.


Oh yeah. One more thing before I go to bed. I remember my experiments with sulfamic crystals. I was only able to bring it into water up to six percent by volume. After that the crystals would reform at well above 3 microns. So when I created a restoration product based on an optical synthetic silica (3 microns), a couple of organic thickeners, and some water;…I couldn’t go above this figure. Nonetheless the acid boosted the effectiveness of the silica by just a very little bit. Which reminds me of a video demo Marc Tanner did for Facebook showing how polishing glass with a superabrasive like cerium oxide can actually work faster than hydrofluoric acid. Remember that is the nasty stuff.

I could write about acids all night. But its ten minutes away from midnight.



This past month I lost a 3 day resi job, to a window cleaner selling my coustomer on an “acid wash” clean! I was puzzled!

I insisted her windows needed only a maintnance clean but she was dead set that her other guy would acid wash them providing a superior clean!

I was actually going to post about this, but now it’s been brought up! What is this acid wash she speaks about?

Hi Sal,

I can’t say of course exactly which acid he was planning on using. But. You could show her the acid test I described in my post here. The one that causes the scratches to become greatly magnified. Then there is the other one that shows how an etchant such as hydroflouric will cause a rippled effect. This should get her attention. There is a third one that I didn’t mention. If you take hydrofluoric even at a 1 or 2 percent concentration, put it in a plastic cup, then set a mirror plate over it, you will get a white etch from the rising fumes. The cloudy etch will take on the circle of the top rim of the cup.

This is one of the reasons I started my blog. To help those who really care to keep their jobs and get more. Also to save their businesses. My blog is set for mobile apps so please feel free to use it any way you can. And definitely show her at least the scratch test. It is quick and should get you your job back and a whole lot more respect.



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I just want to say be VERY careful with any chemicals. Read the MSDS. And wear gloves and eye goggles. Then store your bottles in a safe place.


They are most likely using safe restore or phosphoric acid. You should show the client some articles about untrained use of acids and see if she still wants an acid wash. Unless she has hard water stains on her windows I don’t see why an acid wash is needed. Tell client to find out what’s in the acid wash before it is used on windows because the run off can cause damage to house and frames if not properly rinsed after used. Like Henry said without knowing what acid is be used there is no telling what kind of damage could be done

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