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Farmer John

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Scientifically, why does red fabric turn dark when pressed with a hot iron ?
John
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Jeanette Frantz

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Reply with quote  #2 
John, scientifically, I don't know.  But, once the fabric cools, it returns to its original color -- at least that has been my experience.  Red fabric is one of those colors that tends to "bleed".  This problem, I know, seems to occur more now than it did when the dyes used were organic.  The remedies to stop the bleeding used 20 or more years ago just don't work now because the dyes are all chemical, rather than organic.

I wish I had an answer for your question -- probably just a useless comment by me! 

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Jeanette Frantz, Ocala, Florida
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Farmer John

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Jeanette, I have googled this question, and got these answers...
A.  Because of the heat
B.  Because the fibers are pressed flat and don't reflect the color

The visible light spectrum colors that we see are of various wave lengths.  I suspect that the heat
changes the wave length, so that the color appears darker when hot.  Just a guess....    I do know that it is not due to the fibers being pressed flat because the bright red enameled/porcelain vent of my Coleman gasoline lantern turns a deep maroon when hot.  But why only red ??
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Margaret

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Reply with quote  #4 
Jeannette, your comments are always useful, you know a lot about a multitude of subjects! I wasn't aware of the change in dyes from organic to chemical, although I do remember that blues and reds used to bleed much more often than they do now. I have some real indigo fabric from S Africa (ok, I guess Levis are real indigo, too!) and I've washed it multiple times and still had some bleeding.

John, are you using steam in your iron? I'm sure the water makes the color appear darker - does it to blues, too. I may have to do some experiments of my own! Could be just the heat, though. 

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Margaret 
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Farmer John

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Margaret, I use a dry iron.  I just tried some reds and they darkren without the need to have moisture or steam present.
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Miriam

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Reply with quote  #6 
My red hair goes darker when it is wet except for the gray ones... I haven't tried ironing it - not even back in the 60's...
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Jeanette Frantz

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Reply with quote  #7 
Miriam, I love your comment about your red hair!  LOL!

John, I've had different colors (other than red) increase in color intensity when heat is applied by way of an iron.  Believe me, it's not just reds!

Okay, the timer just went off -- it's time for dinner. 

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Jeanette Frantz, Ocala, Florida
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KenmoreGal2

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Reply with quote  #8 
I have often wondered the exact same thing John. Thanks for posting the question! I only notice it on red fabric.
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redmadder

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Reply with quote  #9 
Thermochromic dyes.  In the case of regular fabric, it is a property of the dye pigments or solvents used to process the fabric.  
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Farmer John

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Reply with quote  #10 
Thanks, Redmatter, that is the answer !!  What a great group of knowledge this is.  There is a lot for KG2 and me to Google about "thermochromism"....here is a small sample...

How do thermochromic dyes work?
Thermochromic paints use of liquid crystals or leuco dye technology. After absorbing a certain amount of light or heat, the crystallic or molecular structure of the pigment reversibly changes in such a way that it absorbs and emits light at a different wavelength than at lower temperatures.

John


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