Rainbow Effect when looking trough tinted glass, complaint

Go2Guy · May 20, 2015

Hello My fellow Tinter,
I’m a long time reader and First time contributer.
This Thread is to help us tinters deal with past/current/future customers, when they complain about Rainbow colors and effects after tinting the glass and/or when they where there polarized glasses.

I recently tinted a 2014 Scion TC and had the customer come back and complain that when he looks through his rear windshield he sees a Rainbow effect. At first when he told me I truly did not what to say besides drawing from 2 previous experiences with this, which were:
1] I had a 1996 Toyota Tercell rear glass that when I was cleaning/prepping it. This was even through there was NO TINT on it yet , It clearly had this rainbow effect [iridescence]
2]When ever I wear polarized glasses in my own car I see this effect

I searched tintdude and found several experiences but no concrete definition as to what it is, how it works and what causes it: So after much research on this on Google I found proof that this is normal and it is called Iridescence which is caused Strain Pattern when tempering/heat treating the glass.

Definition: Iridescence (also known as goniochromism or what we tinters and consumers called the rainbow effect) is the property of certain surfaces that appear to change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, butterfly wings and sea shells, as well as certain minerals. NOTE: This term is Generic and applies to all diffraction's of light trough a given surface however is this inheritant to all Heat treated/tempered glass, which includes ALL TEMPERED AUTO GLASS.

Definition: Strain pattern refers to a specific geometric pattern of iridescence or darkish shadows that may appear under certain lighting conditions, particularly in the presence of polarized light (also called “quench marks”). The phenomena are caused by the localized stresses imparted by the rapid air cooling of the heat-treating operation. strain pattern is characteristic of heat-treated glass and is not considered a defect

So for all the complaining customers out there, this is the solid CONCRETE PROOF for us tinters to show them that this is not a quality control issue of the film or the installer, but instead just the Proven nature of all tempered/heated treated glass. These articles explain how the effect has always been there however is amplified under certain lighting conditions, reflections and polarization

And now the proof for us to show the customers I would recommend printing one of these out :

This is from the Auto Glass manufacture PPG
http://buyat.ppg.com/glasstechlib/32_TD115F.pdf

This is an article for glass manufactures which document this effect and how the glass manufacture can help reduce it but not eliminate, main priniciple is that its the glass manufacture's not the tinters fault
http://www.glastory.net/iridescence-dealing-with-strain-patterns/

This is a list of search results from google on the subject
https://www.google.com/search?num=50&q=IRIDESCENCE+in+tempered+auto+glass&spell=1&sa=X&ei=jbRcVZ-xLMeyogTTrYEw&ved=0CBsQvwUoAA&biw=836&bih=856

This is an article from Old Castle Glass [a major glass manufacture, which is my fav as it is simply explained]
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&ved=0CEkQFjAF&url=http%3A%2F%2Fasint2.ki.com%2Fprod%2Fpkb%2Fpkb.nsf%2F113c13b71d41aebf86256e68005c904a%2F16ce876d92ad927b86257bd4006c387d%2F%24FILE%2FStrain%2520Pattern%2520Observed%2520in%2520Heat-Treated%2520Glass.doc&ei=795cVeeQNoSMNvPOgPAI&usg=AFQjCNHhE4okkn5IMKmNkFMB6qT2DTG3pA&sig2=zT3uJlDx-SPkTU0XZwg91Q

vquestfilms.com · May 20, 2015

:thumb Nice research! You are starting out in this forum with a great habit, keep it up. :beer

I always tell the people with Polarized glasses to just look at a piece of clear tempered and that usually solves the issue...

Go2Guy · May 20, 2015

This is the article from Old Castle Glass [a major glass manufacture, which is my fav as it is simply explained]
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&ved=0CEkQFjAF&url=http%3A%2F%2Fasint2.ki.com%2Fprod%2Fpkb%2Fpkb.nsf%2F113c13b71d41aebf86256e68005c904a%2F16ce876d92ad927b86257bd4006c387d%2F%24FILE%2FStrain%2520Pattern%2520Observed%2520in%2520Heat-Treated%2520Glass.doc&ei=795cVeeQNoSMNvPOgPAI&usg=AFQjCNHhE4okkn5IMKmNkFMB6qT2DTG3pA&sig2=zT3uJlDx-SPkTU0XZwg91Q

Strain Pattern Observed in Heat-Treated Glass

An iridescent coloration that is observed in heat-treated glass occurs as a result of a strain pattern that is present in all heat-treated glass. However, it is observed only at certain viewing angles, when the glass is in a partly sunny environment, and highlighted against a darkened background.

A strain pattern is created in all heat-treated glass as a result of rapidly cooling the exterior glass surfaces once the glass exits the 1230⁰F furnace. Since the glass center cools slower than the exterior surfaces, compression and tension zones are created within the glass body. This causes a strain pattern to occur throughout the glass, and an invisible iridescent coloration occurs wherever the high velocity quench air first contacts the hot glass surface. The effect of refracting the light in this manner is called birefringence, and it is readily observed when viewing heat-treated glass through polarized sunglasses. It is often seen without polarized glasses on many rear car windshields. The strain pattern, which is considered normal for heat treated glass, is usually invisible in most glass products. However, certain seasons of the year such as spring and fall, allows the effect to be readily observed due to the sun’s position as it crosses the horizon. Also, some tinted glass colors exhibit a significantly greater propensity for allowing the strain pattern to be observed, than all other glass colors. Those colors are blue, blue/green and green. It is unusual not to observe the strain pattern in these heat-treated glass colors.

The iridescence effect being viewed in the glass is not discoloration caused by a defect in the glass, nor by a fault of our processing procedures, but rather, it is caused by a strain pattern which is inherent in all heat treated glass. Because the iridescence is a well-recognized anomaly that occurs in all heat-treated glass, the ASTM (American Society for Testing and Materials) organization, which governs the quality requirements for the heat-treated glass industry, addresses this effect in the ASTM Specification C-1048 as follows;

Paragraph 7.5 Strain Pattern -

In heat-strengthened and fully tempered glass, a strain pattern, which is not normally visible, may become visible under certain light conditions. It is characteristic of these kinds of glasses and should not be mistaken as discoloration or nonuniform tint or color.

The National Standard of Canada Specification CAN/CGSB-12.1-M, Type 2, which governs the quality requirements for the glass industry in Canada, indicates the following concerning the observed strain pattern in tempered glass produced throughout Canada.

Paragraph 8.3 Strain Pattern-

In glass, a strain pattern that is not normally visible may become visible under certain light conditions. This is characteristic of these kinds of glass and should not be mistaken for discoloration or non-uniform tint or color. Strain pattern shall not be considered as a defect.

Oldcastle BuildingEnvelope™ and other major glass fabricators’ documents canvassed throughout the United States, Canada and Europe -- all indicate the presence of a strain pattern in their heat-treated glass. Data taken from the Sweets Catalog and from our competitor’s technical manuals as well all specifically address the occurrence of a strain pattern typical to heat-treated glass.

The strain pattern is observed due to the incidence angle that light strikes the glass surface, and is refracted through the compressive and tension layers in heat-treated glass. This causes the visible light spectrum, which consists of colors (occurring in the 400 to 700 nanometer wavelength range), to dissimulate, into hues of grey, black and sometimes red when viewed in reflectance at the glass surface. Upon viewing glass that is silhouetted against background lighting of lesser intensity, the dissimulating hues become highlighted when viewing at angles other than perpendicular to the plane of vision.

The reason the effect is more pronounced in some tints than in clear glass and other tinted glass, is explained by the Young –Helmholtz Theory on Color Vision, which states,

“The existence in the eye of three mechanisms, each sensitive to one of the three primary colors, red, green and blue, accounts for some of the observed phenomena of color vision”.

The Young-Helmholtz Theory suggests that the strain pattern would be equally visible in a red tinted product if it were heat-treated.

Typically, glass viewed at eye level and perpendicular to the field of vision, does not exhibit the strain pattern. This effect can only be seen when viewing glass at acute or obtuse angles to the field of vision, or at uneven planes. Both the ASTM C 1036 and ASTM C1048 inspection procedures are very specific for viewing glass, which states, “the observer must view the glass perpendicular and normal to the glass plane”.

The installed heat-treated glass having a strain pattern is considered normal, as the aesthetic effects observed do not compromise the required strength and performance characteristics of the glass product.

Go2Guy · May 20, 2015

Thank you vquest

Research is an obsession of mine and most of the time i can't stop until I find solid understanding of the topic im researching. I have spent many hours Researching Tintdude, however never felt I had anything worth contributing until now, [You guys are all experts] I hope this solves future customer complaints Im going to print one out and keep at my shop. Again thanks

EWF · May 21, 2015

Nice research! You are starting out in this forum with a great habit, keep it up.

Echo from EWF !! Great post. I hope to see you around here often with informative content like that.

Regards,

Howard

Go2Guy · May 21, 2015

Thank you EWF,
I've read many of your post's and I compliment you on your informative content as well.
Ironically I just asked you some questions on another thread about Gareware[i love them!!!!]. . . . As stated research is an obession of mine, So are high quality products for good prices, Hence the reason I LOVE GAREWARE.
Again Thanks Howard. . . .