Hidden Scratches

Scratches, Point Indent Fractures, and Blemishes are easily hidden by dirt, and hard water spots.  But once the window is cleaned they come into full view.  Especially in the direct sunlight.  Although depending on the lighting they are even more noticeable at night.  This is the reason why it usually is the window cleaner who is blamed.  No one even knew about the scratches until they were revealed.

I will tell you just one of my scratch stories.  I was called out to a new multilevel building by the general contractor who built it.  He had the windows cleaned professionally soon after they were installed.  Which windows had been stored at least six months at another site.  Once the windows were cleaned some rather heavy scratches were revealed.  Razor blades were used.  It was my job to save or sink the window cleaner.  The first thing I did was clean the window with the most scratches.  I did not use a metal razor at this time.  Next I inspected for what has been called glass fines for many years.  The simple truth is we all know some type of raised defect is present.  When the surface is scraped or even rubbed with something else, this defect can be removed and dragged causing scratches.  There is a rather basic grassroots test for identifying what I call the ghost particle.  Here are a couple of videos I made  demonstrating the test using a penny.

Another way to "feel" the glass surface is to flip your hand around so you can lightly run the flat of your fingernails across the glass.  You will be amazed what you can actually learn from this method.

To finish the story I was able to immediately learn the windows were loaded with some very large (although invisible to sight) defects.  In theory the scratches could have easily been caused by such defects.  But I didn't want to leave matters unknown.  At least not completely.

Upon closer examination I noticed that all of the scratches ran north to south.  So up and down.  They almost looked parallel.  So I asked the GC if he didn't mind if I created some more scratches.  He said no.  So I took a metal hand held razor.  The blade was steel.  With this I wet the window with soapy water and did my best with all my strength to scratch the window.  Running the blade at a ninety degree angle opposite the direction of the scratches already present.  Then I cleared the window with a squeegee to inspect for any scratches that ran in the opposing direction.  There were NO SCRATCHES!  

Obviously this completely clear the window cleaner who I assume was very happy when they heard my report.  Although I am also sure they probably are much more careful now.

I made mention to the GC that this problem could have been caused in storage when the plates were dragged across one another.  If they were stored horizontal on top of one another having not been set with interleaving materials to keep them separated, then there might have been sand particles in between that would have scratched.  (Glass plates are supposed to be stored vertical and separated so they don't rub or develop moisture.)  Sand is mostly silica the same as glass.  Glass is actually made from a very special type of silica.  I am sure for this reason it is very easy to scratch glass with a piece of broken glass.  And should also be as easy to scratch with sand particles.

Here is a picture of some very light scratches on a window once the dirt was removed.  It was in the direct sun when I took the picture.  I very much doubt these scratches would be easy to see on an overcast day.  But very easy to see on a bright sunny day and a clean window.  Further you can make out the scratch pattern that shows how wide the razor was.  But again this surface was scratch sensitive with defects that were the cause of the scratches.

Henry Grover Jr.

henrygrover222@gmail.com

Glass Smart Inspection Services