Micro-Crystalline Silica for Glass Restoration

At less than 50 cents per pound micro-crystalline silica certainly is in competition with cerium oxide and many other polishing superabrasives.  Cerium is up to eighty bux a pound. But don't be fooled. micro-crystalline silica does have its drawbacks.  The biggest is cancer.  It is a carcinogen.  In powder form that is.  For this reason silica powder is not sold by many companies.  Instead they sell colloidal suspensions of micro-crystalline silica.  Whether that be a powder made by crushing naturally occuring minerals/rocks.  Or a man made amorphous silica.  When silica particles are suspended in fluid dispersions it is hard to breath them in.  Which is the primary way they cause cancer. 

Some guys will polish glass dry.  This releases a glass dust.  It is not crystalline.  But the particles are microscopic.  Usually around 3 microns in size.  Because the size of the silicon carbide or SiC used in the polishing pad is close to this size.  If you do this type of work you should absolutely wear the best protection possible.  That being a face mask that will block a particle of this size.  Such a face mask should also be used if you are creating a slurry, colloidal suspension, or compound based on a micro-crystalline particle of this approximate size.

Micro-crystalline silica as was mentioned here is found in nature.  It usually includes other minerals too.  These are what give the rocks different colors.  Such as rose quartz.  The silica that is closest to being just SiO2 is the most transparent.  It is the most pure.  Micro-crystalline silicas will have different crystal structures and different shaped particles.  Hence they will have different hardnesses too.  The purity rating is based on an average particle size.  This is shown on a line graph.  Say for example that the product is 95 percent 2.4 microns.  That means that the other 5 percent is slightly less than and greater than 2.4 microns.  You will also see the spread of elements such as iron, aluminum, and carbon that likely will be present. There should be a percentage for each of these listed.  The crystal structure will be given, and the morphology of the particle. 

It can be very dangerous how a slurry, colloidal suspension, or compound based on a micro-crystalline silica is used on glass for light stain removal.  If a safe technique is not followed it is too easy to leave what I call a "scratch haze".  In theory it is much more easy to do this with micro-crystalline silica rather than cerium oxide.  Cerium is used to create a superior surface. A general rule to follow is to keep your felt flat on the window at all times, keep it moving slow (maybe only around 1,000 rpms), and watch your pressure.  You absolutely NEVER want to lift up the edge of the polishing pad and rip into the glass moving up and down, left to right.  This will most certainly create a scratch haze that will be totally invisible in the shade or on a cloudy overcast day.  It will however be quite visible on a bright sunny day.  Especially on the second story glass.  To help with this technique I have shown how a "wobble wheel" can be built and used with various pads such as those made of felt. 

 Sometimes you might be working on specialty coatings on glass such as low e reflective first surface products.  Some low e first surface coatings are hardly noticeable at all.  As this technology gets better it will be even more difficult to quickly identify them by sight alone.  It is not possible to use some of the more aggressive stain removal techniques for removing mineral deposits from such coatings.  The "lighter touch" is absolutely critical for working with these problem situations.

The first newsletter called the Product Development Review focuses on light stain removal.  These issues come out once a month.  The second issue I have produced is on a product I call Soap N Seal.  It seals glass when you clean the window.  No extra time is required.  These issues are 35 dollars each.  They contain the formulas for making these products yourself.  And list the sources for all the ingredients.  If you want to subscribe just send an email to henrygroverjr@gmail.com

Written by Henry Grover Jr.
Producing the Product Development Review

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