You need to do some research because that patent has definitely NOT ran out. USPTO.GOV is your friend.
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Either way, I've tried multiple different clays side by side. They're NOT all created equal.
If all the clay you bought was made in America, it was all the same. Now if you're getting your clay illegally, that's your issue. The patent house doesn't lie. All you have to do is look it up. It's not my word, it's the U.S. government's word. They would know since they issue the patents.
I've had some time to look through the patents. They're actually Japanese it seems, and there's multiple patents, one ran out earlier this year.
Even if they are all from the same place, I'm betting there's different grades of the stuff. That would explain inconsistencies of clay from different labels.
GRADES are not what I'm talking about. There are 3 different grades. Consumer grade clay, which is what you find over the counter. Medium and aggressive grade clays are only found at body shop supply outlets or similar businesses. So yes, the grades are different but the MANUFACTURER who owns the patent in the USA is Auto Wax.
Then at the very least i find the grade of clay mother's uses its too aggressive. It catches too easily, smudges more, and marrs.
The only clay that Mother's sells is consumer grade.
I've been doing this since before clay was invented and have used my fair share of various grades of clay. In all my travels, I have not noticed any difference between the same grade of clay offered by different companies. Clay is going to perform differently on different surfaces because of the amount of contamination present. Had you tried various clay brands on the SAME car, that would be one thing but to claim that one brand mars more than another means that you were either using two different grades of clay or you're imagining things.
Yes I have tried both on the SAME car. A first gen NA miata, the owner was working with me to speed things along. Single stage paint, way softer stuff. He noticed it too, we swapped clays with each other back and forth a few times to confirm.
Mother's clay more aggressive than griot's clay. Both pieces were new when we began, and both colored a very similiar yellow. By the time we were done, the griots piece was a darker yellow, while the mother's pieces seemed to be taking in some red (the paint color).
Well, I know for a fact that all clay made and sold in the USA is the same. I don't know what else to tell you as the links that I provided back that up.