Microlapping Window Glass

This is a relatively simple process using either a cerium oxide slurry or some other optical grade polishing powder with water.  It is possible to do by hand.  Yet a circular felt pad works exceptionally fast.  Another machine that can be used for this is a square random oscillating sander.  Just remove any pad or bottom attatchment and slap a thick piece of hard felt on.  It will polish the glass without throwing compound fifty feet.  In fact it is so neat you can work right up to a quarter inch of another plate without getting any slurry on it.  All you want to do is remove a very slight amount of glass.  Just enough so that when the window is fogged you don't see any patterns or lines.  A more simple way of testing the new surface is to wet it with pure water.  If it has been properly microlapped the water will sheet over the entire surface equally.  It will not bead up at all anyplace.

One reason why you might want to microlap is to set up the surface for a hydrophobic, or even a hydrophylic coating.  The coatings which form a true chemical bond to the glass will likely require as many free oxygen atoms as possible.  So you won't want any organic or mineral residues blocking the reactions.  The exterior of window glass also undergoes a certain amount of corrosion or weathering.  Weathering is the more correct technical term that glass scientists use.  If the etch that happens is static then there will be invisible deposits that will block chemical reactions.

If you doubt that weathering happens try this.  The next time you are working on an old set of storm windows try running your finger lightly over the inside and outside surfaces of the upper storm.  Make sure both surfaces are perfectly clean.  You will detect a noticeable drag on the outer surface.  By comparison the inside will be very smooth.  You will note then that the outer surface has undergone extensive weathering.  Usually this type of etch is dynamic.  But depending on various conditions it could be partly static too.

Written by Henry Grover Jr

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