A Glimpse of the Ghost Particle?

For decades now it has been the belief of the Window Cleaning Industry that fabrication debris or microfines are the reason for defective glass surfaces which are rough and are very easily scratched during the cleaning process.  It is in fact still the belief of many that this happens in the tempering factories where it is said the glass picks up the particulates of glass resulting from the cutting process before the sheets are tempered.  Then these particulates and possibly other particulate debris are by means of the rollers in the tempering oven, driven into the semi viscous flat glass surfaces.  Where they essentially fuse once the glass cools down to room temperature.  Is this the truth or is it a misguided lie?  If you ask most Window Cleaners you will learn very fast that they don’t care.  They simply would like it stopped, and have some means of working with the defective glass that has already made it into buildings all over the world.  They have become totally exasperated by the lawsuits that have resulted and the burden of dealing with this problem.  Which by the way is absolutely not limited to the use of metal razor blades.  I have personally witnessed defective surfaces scratched by plastic 'blades', and 0000 steel wool.  I have also heard reports of scratching resulting from soft cotton cloths!

For many years now the Glass Committee of the International Window Cleaning Association (IWCA) has been focused on learning what the real answer to this problem is.  It couldn’t be more obvious to everyone  within the Window Cleaning Industry and the Glass Industry that this is a problem.  What we all would like to know is precisely what it is, and how can it be stopped?  Also, can the damaged surfaces which are already installed actually be repaired?  The IWCA deserves the full support of every single window cleaner in this world.  Simply because they have taken on the challenge and the burden of getting the scientific answers to these questions.  Spearheaded by Paul West and Paul Duffer, along with the help of others, they have spent many hours and dollars setting up special tests to learn the truth.  The last series of tests just finished involved attempting to embed and fuse glass microfines into a semi viscous plate of glass during the tempering process.  In this they failed miserably.  Yet they succeeded in my opinion in proving that the old idea about microfines and tempered glass is quite wrong.  There is something else at work here.  Now I know this is absolute heresy to many people.  So I am not going to win their applause.  But let me present you with some very interesting ideas.  Some of which you might not be aware of.

The only other process to look at is the float process.  It is called the float glass process because the glass actually floats down a river of molten tin called the ribbon.  This is where flat glass is actually made.  The float glass line was originally developed back in 1959.  One year after I was born.  

                                                        

Each line/factory will produce 300 to 600 tons of product a day.  It begins by heating the batch of silica, limestone, soda ash, dolomite, and cullet to about 2900 degrees Fahrenheit.  In a matter of minutes!  So far so good.  Next the melted glass goes through the fining process.  During this 'fining' process bubbles that result from the melting of the batch actually rise ‘to the surface’ and escape into the atmosphere of the furnace.  In fact it was stated in one of the videos I watched that the processes within the furnaces are managed from the control room to ensure that the glass is homogeneous and free of bubbles.  This is interesting.  I could ask several questions at this juncture.  Another interesting statement made was that heating in the float bath is carefully controlled to ‘melt out’ any roughness in the glass.  In fact to produce excellent quality glass one must control its cross ribbon temperature and associated viscosity. 

When the glass passes onto the liquid tin bath it is around 1900 degrees Fahrenheit.  It leaves the float bath at about 1,000 to 1,100 degrees and enters the annealing oven or lehr.  It then comes out of the other end of  the annealing oven at between 200 and 350 degrees.  I know some of you are mouthing the words rollers at this point.  But the manufacturers state that once the glass comes out of the float bath chamber at 1,000 degrees it is hard enough so that the rollers that move it through the annealing oven cannot do damage to it.  Checkout this video of a company called Stewart Engineers.

                                                          

They state on their website that annealed glass should not be allowed to vary more than five degrees.  So the rate of cooling as it passes through the annealing lehr must be very closely controlled.  If you check out the control room on the Pilkington video I have embedded here you will notice it looks more high tech than the Bridge of the Enterprise in Star Trek.  Not for no good reason!  Sure it is just a ribbon of glass.  But all of the processes  involved in controlling the flow rate, temperature, and the chemistry of the barrier gas in the float bath chamber;...must be very carefully and precisely controlled.

Oh yes.  I haven’t mentioned anything about the chamber gas of pressurized hydrogen/nitrogen yet.  Very simply put, the reason for the use of this gas in the float chamber is to prevent oxygen from contaminating the liquid tin.  This however does have a direct effect on the glass surface.  There is actually an exchange that goes on consistently between the chemistry of the tin and that of the glass surface.  Such that even the mechanical hardness of the tin side is greater than that of the air side.  Which has been proven by a very accurate scientific test.  A harder surface is not necessarily a bad thing which it isn't, but consider this statement made by Weissmann Rudolf in a paper called Fundamental Properties of Float Glass Surfaces;  “...the tin and atmosphere sides show a slight difference in their strength that comes from the contact of the tin side with transport rollers. In addition, since the ribbon is molten and deformable along almost the whole length of the bath, any specks falling from the bath atmosphere or any bubbles rising through the molten tin will permanently damage the surface.”.  Now that last sentence is worthy of note.  Specs from the bath atmosphere falling onto the surface or bubbles rising to the surface.  Remember that ‘bath atmosphere’ is a pure nitrogen/hydrogen gas under pressure.  Here is a very interesting statement from Walker Textures, a company that specializes in professionally etching glass and mirror.  “Float glass is best etched on the 'atmosphere' side of the sheet, due to the increased likelihood of impurities and/or surface imperfections on the 'tin' side of the sheet.”.  If their customers want the glass etched on both sides they will not guarantee the quality of the entire job.  Just the air side.  Not the tin side.  At this juncture I will quote Stewart Engineers .  They state, “All tin baths are uniquely designed and operated which results in a wide variance of glass product quality.”.  In fact the technology used in the float glass process is considered intellectual property, and is licensed.  Float lines cost about 120 million to build new, and cost about 360,000 to rebuild.  Which must be done every 10 to 12 years.  There must be a good reason to rebuild after ten years.  Also if you have one that is producing high quality glass, I don't think you would be so inclined as to tell your competition about the details of its operation.

So there you have it.  Are you beginning to get a glimpse of the Ghost Particle?  Did you know that the UK and other Countries are very familiar with defective ‘float glass’ surfaces?  Why they even have a classification system for the different individual defects/inclusions.  This box was created by a company called Dark Field Technologies.  

This next picture was taken with a polarized microscope from Leica Microsystems.

Leica sells many different types of microscopes, also polarized microscopes which are favored by glass inspection companies that specialize in detecting surface defects/inclusions.  Which can also be seen when they are just below the surface using a polarized microscope.  As in this colorful picture above.

  

This next picture is a Scanning Electron Microscopic image of a nickel sulfide inclusion.  It came from the website of a company in the UK called Glass Technology Services.

  
Stones, knots, cord, ream, blisters, seeds, airlines, metallic inclusions, and raw material contaminants.  These are all terms JTF Microscopy Services uses to identify various glass defects.  They also use Polarized Microscopy.  Checkout this somewhat scary picture below.  It is an SEM (scanning electron microscope) image at 3,000x of a wafer defect taken with the e-RAM.  Taken by a company called SEM Tech Solutions. 

The same company also created this very colorful Birdseye 3D image at 3,000x of the preceding SEM image taken with the e-RAM.

I would like to quote Kathryn Gromoski of Penn State 2010 in an article she wrote entitled, "Glass Breakage-Nickel Sulfide Inclusions".  "It is at the very beginning of the life of the glass that inclusions are introduced. Inclusions are microscopic particles that are incorporated into the structure of the glass in the initial heating process. According to the Glass Association of North America (GANA), there are approximately 50 different types of dirt or other inclusions recognized, but almost all of them are completely harmless (Johnson 2008). Nickel sulfide is the only exception, and even then it is only a problem in tempered glass.".  

Here is the link to the entire article

https://failures.wikispaces.com/Glass+Breakage+-+Nickel+Sulfide+Inclusions 

Notice that she states that these particles are introduced at the very beginning of the ribbon.  Not during the tempering process.  She also does NOT call them defects but rather inclusions.  Although as inclusions they are still 'microscopic particles'.  Of which there are about fifty different kinds.  That is a virtual zoo of particles!  But even so they are still quite harmless.  By whose standards?  By the glass manufacturers of course.  Unless these happen to be nickel sulfide inclusions they won't cause glass breakage.  Even nickel sulfide is considered harmless unless it ends up in tempered plates down the line. Only then can it cause breakage.  Simply put glass manufacturers do not want to see these inclusions or microscopic particles as a defect.  The microscopic quality of the surface of float glass (which is recognized by different industries as the tin side) is not really very important.  As long as the glass isn't going to spontaneously explode or the window implode, the glass manufacturers are cool with it.  There might be a problem here if it was not so easy to coat the air side of float glass.  The air side which faces up is coated right on the tin bath.  This brings me to another interesting thought.

It is the practice of the glass manufacturers to NOT coat the tin side.  Also the coated (Low E) side is usually facing in on IG (insulated glass) units.  That is either the 2nd or 3rd surface. Which means the tin side will be facing out.  There is a special UV lamp which is used to locate the tin side.  This is significant because if the tin side were facing in we likely would not have many defects (or inclusions) to deal with.  Although it is good to remember here that it is possible for 'specs' to fall onto the air side of float glass in the float glass chamber.  This happens when the chamber air becomes contaminated by the tin.  

Now lets take a look at what the IWCA has been up to.

Under the direction of Paul West, the chairman of the Glass Committee, there were several different samples of windows with and without scratches taken from different parts of the country, and submitted to Penn State University as a summer project.  The purpose of this project is to learn why some glass surfaces appear to be more rough than others.  Also what are the actual features of such "rough surfaces" that cause window cleaners to make this claim? At one facility it was learned that some glass scratched and other glass on the same building did not scratch.  The obvious question is what are the underlying surface properties that could account for this?  Another question would be, is there something unique about certain glass surface properties that make it easy for amorphous silica and silicate particles in the environment to scratch such a surface?  Also, might these surface properties be responsible for the variety of scratched windows mentioned earlier?  Further, are these questionable surface properties connected only with heat strengthening and tempering of glass? Or are such rough problematic surfaces formed on the tin side of the float glass ribbon early in its life?

This very specialized field of glass defect/inclusion analysis and inspections is a technology that I will continue to explore. There will be more articles that I will be writing on the 'Ghost Particle' that will be posted in this blog.  This is just the beginning.  I think you all have realized by now that this problem is here to stay.  As Window Cleaners we need an accurate understanding of exactly what the Ghost Particle is. We know at this juncture that it absolutely is not a ghost.  It is in fact quite real.  It is also likely that it will have multiple identities.  I truly do not believe in ghosts anyhow.  We also desperately need to be better equipped to accurately identify the condition and quality of the surface of the windows we are working on. Those which are prone to scratches should be discovered before installation of course.  However if such problematic windows have already been installed, we also need to have methods for working on them as safely as possible with the best tools and green chemicals.  Lastly I have heard that it might be possible to perfect a system/method for restoring these surfaces by grinding, polishing and sealing with a scratch resistant silane.  More on this later.

I would like to take this opportunity to thank the IWCA Glass Committee and all its members for taking the last eight years to explore this very important issue.  It has a direct impact on every window cleaner in the world.  For this reason everyone should become members and support the educational work of the IWCA. 

International Window Cleaning Association
Mr. Paul West / Chairman
Glass Education Committee
1100-H Brandywine Blvd
Zanesville, OH 43701-7303
800-875-4922 / www.IWCA.org

Stewart Engineers
11640 NorthPark Drive, Suite 100
WakeForest, NC 27587
(01)-919-435-9100 / www.StewartEngineers.com

Dark Field Technologies
70 Robinson Blvd.
Orange, CT 06477
203-298-0731 / www.darkfield.com

Walker Textures
9551 Ray Lawson, Montreal QC
Canada H1J1L5
888-320-3030 / walkerglass.com

Leica Microsystems
1700 Leider Lane
Buffalo Grove, IL 60089
800-248-0123 / leica-microsystems.com

Glass Technology Services
9 Churchill Way, Chapeltown
Sheffield, South Yorkshire
S352PY United Kingdom
44-(0)-114-290-1801 / www.glass-ts.com

JTF Microscopy Services
9064 Wixson Rd
Hammondsport, NY 14840
607-731-8863 / jtfmicroscopy.com

SEM Tech Solutions
6 Executive Park Drive
North Billerica, MA 01862
978-663-9822 / semtechsolutions.com
Written by Henry Grover Jr.
henrygroverjr@gmail.com
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The Cause of Scratched Glass-A Quest for Answers By Paul West

Send your email for a copy of the Glass Smart Insider to henrygroverjr@gmail.com

For decades now, window cleaners have reported encountering glass with a “rough surface” that has a “drag sensation” and exhibits a “tinkling sound” when a razor blade is passed over the surface.  This type of surface has historically been described as  fabricating debris in varying amounts. Historically, “fabricating debris” has been described as particles that were not adequately washed off prior to entering the tempering oven, thus getting fused or “baked” onto the surface. However, research by the IWCA in recent years has shed light on some inconsistencies in that theory.

First, lab tests that attempted to fuse glass particles and sand to flat glass failed. After heating and cooling glass contaminated with particles failed to produce the fusion.

Second, powerful microscopes attempted to detect fused particles on actual samples of offensively scratched glass from the field. No such particles could be identified.

Third, after more than five years of searching, no actual physical specimens of glass tainted with fused fabricating debris have been delivered to the IWCA. However, we were able to gather scratched glass samples from actual construction sites in all parts of the country.  Sure enough, these scratched glass samples exhibited a “rough surface” whereas many times similar glass windows on the same job site exhibited a smooth surface and did not scratch even though the same cleaning methods were used.

Fourth, at last years IWCA Convention we introduced the idea that the rough surface of glass that appears more likely to scratch could be due to a change at the micro or nano level, and the term nanoscale roughness was introduced. There is an entire field of science that discusses how surfaces with a nanoscale roughness may be more prone to physical damage.  The question remained however - how do the “rough surfaces” that are encountered in the field originate? Do they develop during the tempering process? Or are there other considerations? Could the development of such nanoscale roughness go back to the actual float glass process where glass is made on a bed of molten tin - producing what is known as an “air side” and a “tin side”?

It is interesting to note in the IWCA collection of scratched glass with “rough” surfaces the tin side usually corresponded with the rough side, which corresponded with the scratched side.  Should this surprise us? Is it possible that the tin side of float glass can develop a "random roughness"?

To begin to understand this, I direct your attention to the paper “Statistical Analysis of the Metrological Properties of Float Glass” by Brian W. Yates and Alan M. Duffy. This paper speaks of a “surface roughness” that develops on the tin side of float glass and reports “It can be seen that the overall tin side surface roughness average is indeed rougher on average than the air side”. The conclusion reads: “Statistically significant differences were found between the tin and air side surface roughness values for both untreated and acid treated, with the tin side being significantly rougher than the air side.”

Is there a definite link between the rough tin side of some glass surfaces and surface scratching? Does post production heat treatment of glass exacerbate the roughness of some glass surfaces? These questions will be closely examined as you are about to see.

Armed with this knowledge, questions and the collection of scratched glass samples, the IWCA has embarked on the first of its kind scientific research during the summer of 2016. Dr. Paul Duffer has led the way for the IWCA to participate in a special research program at the world class Department of Materials Science and Engineering at Pennsylvania State University. Professor Seong Kim, phd  is dedicated to materials science and has much experience with glass surface studies. He will oversee the IWCA research of scratched glass at Penn State.

The IWCA is dedicated to helping window cleaners better understand the glass surfaces that window cleaners work on daily.  Armed with knowledge as an industry we can develop cleaning methods and practices that will assist us in maintaining the integrity and beauty of glass, reduce possible damage, and adequately protect ourselves should aggressive cleaning techniques and restoration become necessary on a job site.

Please, stay tuned.

Paul West

IWCA Glass Committee Chair

kohalapaul@gmail.com

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