Glass Etchants

Glass etchants such as hydrofluoric acid, sulfuric acid, and ammoniumbifluoride;...should NEVER be used in glass restoration work! Many people will however use them because they are an exceptionally easy and inexpensive, but temporary "fix". Therefore several commercial products have been developed which are based on such chemicals. The reason why they work is the same reason why they should never be used. They go after silicon based molecules with an insatiable hunger. When water spots will not yeild to some of the other acids such as hydrochloric, sulfamic, citric, and acetic it is probably because they are based on silicate minerals. Spots that are based mostly on carbonates will yeild to mild acids like acetic which is in vinegar. Glass is based on a silica/silicate matrix. So acids such as hydrofluoric will attack hard water spots and the glass surface simultaneously. Every time. HF will actually break the SiO2 bond in glass.  There are four different stages of etched glass. Each one has its own appearance. These four are divided into two groups of two. Static and dynamic. Static etch stage one and two shows up as a white cloudiness. Stage one and especially two dynamic etch shows up as a clear distortion of the glass surface. I have seen many times what I call spot imprints. Having the same exact outline shape as the spots that were removed by the etchant. As it turns out the etchants used tend to degrade glass more where the largest concentrations of minerals are. Leaving an imprint. I have proven this in many different ways.

Here is an interesting experiment using hydrofluoric acid and a small light bulb.

Another interesting thing happens when glass etchants are used on solar hardcoats such as PPGs Solar Cool glass. HF in particular has the ability of degrading the physical integrity of the thin film. Sometimes without even showing it. Not until someone comes along with an optical grade polish such as a cerium to remove the newly formed spots, does this become known. It could be that the hard coat will strip right off in patches. One company I worked with had this problem. They had to turn to a very fast machine, a feather touch, and an optical grade submicron aluminum oxide powder.
Anyhow, my techniques are a lot more involved than doing a quick acid wash. The goal is to remove the mineral deposits without doing any damage to the glass surface. At times it is necessary to create a new "near surface". Yet this should be done in a controlled way. Such work requires a price of between ten to twenty dollars per square foot. Most people simply choose to look out dirty windows. It is also true that most times the cause of the stains cannot be completely eliminated. So instead of a one time fix forever, the building becomes what I call a maintenance restoration job. This involves correctly and safely removing the spots, sealing the glass to keep future spots from sticking as tenaciously to the windows, and removing all future spots on a periodic basis along with maintenance of the sealant.

Written by Henry Grover Jr

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Power Washing

Power washing can create stains on glass caused by hard water, cleaning chemicals based on alkalies or acids, or even bleach reacting with paint. Once stains have baked on the glass surface, it is in need of restoration. Certain mineral acids like hydrofluoric, and sulfuric will permanantly etch the glass however. These acids are also used in cleaning bricks. I remember running into a company that used HF to remove paint from a building/home. Which is another application. Only to wind up etching every window. I will also never forget one resty job I performed which I got as a result of a power wash problem. It was a white haze left from a commercial product based on sodium carbonate and sodium metasilicate. These are alkalies, not acids. They did not etch the surface. But they caused a problem nonetheless. It was not a simple fix! I ultimately had to resort to diamond compound and paper towels;...by hand. So the next time you decide to power wash your vinyl awnings, or prep the exterior of the home for painting;...think again. You could be creating a real problem. The best thing is to have me check out the power wash solution. Then have the windows cleaned immediately after the powerwash.

Written by Henry Grover Jr

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Removing Scratches

Contrary to popular opinion, scratches on window glass surfaces can be removed. Even those that are deep enough to catch a fingernail.  There have been many machines developed over the years to accomplish this. But the professionals who perform this service use a combination of these, including their own hybrid systems. Simply because the different scratched glass problems out there are quite varied. There are scratches occurring in patterns at restaurants left by little greeny scouring pads. These are the easiest to remove. Hair line scratches from fabrication debris on tempered glass although rather light most times, can be very time consuming since it covers so much area. Deep grooves caused by diamond rings or broken beer bottles used by vandals are a much more intense problem. These can take upwards of five different steps to completely remove. And there can be some distortion. The bottom line is always time. If the amount of time required to remove the scratches demands a price that exceeds what is reasonable compared to replacement cost, such will preclude performing the service. The objective of the professional then is to choose a system and technique that will completely remove the scratches in the least amount of time possible. This is a highly specialized service. It is in fact a specialty type of glass restoration. Also included in glass restoration is the rejuvenation of etched glass surfaces, and the removal of mineral deposits. Meaning surfaces that have been damaged by hard water deposits. The grinding and or polishing procedure is used to accomplish all three services. Scratches, etched surfaces, and mineral deposits. I can deal with all three. But also have other specialists I can call in if necessary.

Written by Henry Grover Jr

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