Amber Colored Mineral Spirits (Used)

I've been using this '1/8" method' to clean the brushes I use for oil based primer. The primer is Zinsser Cover Stain, just white, no tint.

https://www.youtube.com/watch?v
vDbKBTbic
I collect the used mineral spirits in a jar and let the primer settle out so I can recycle the mineral spirits and use it to clean the brushes again.
I've found that instead of the mineral spirits being clear after the primer settles to the bottom of the jar, it is sort of an amber colored clear. I don't think it's a matter of not waiting long enough because I've gone weeks without touching the jar.
The recycled spirits seem to work just as well as new spirits for cleaning brushes, but I'm curious as to why it is no longer clear. What is in the primer that would cause the spirits to turn amber?
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linseed oil
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On 5/20/2018 11:06 PM, DerbyDad03 wrote:

Do you remember chemistry class, some ingredients settle and separate others remain mixed.
I typically keep two jars of MS. One for the initial cleaning and the second to clean out the other colored stuff that has not settled out of the first.
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On Monday, May 21, 2018 at 10:22:21 AM UTC-4, Leon wrote:

Yep, that's why I ask *what* is in the primer that turns the MS Amber. ;-) According to dadiOH the answer is "linseed oil".

Yes, my final rinse is with new, clear MS which typically results in a virtually clear residual.
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The oil isn't the primer; it is the binder - what keeps the primer in place on the wall after it dries.
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