Reducing the percentage of aluminum stearate in paint.

Hello there,
Unless you already are a professional enough artist to notice such minute differences, I would advise you not to bother with this aspect at all.
Manufacturers use it to streamline the consistency and improve the stability of oil colours over long time. 
It still is (hopefully for good brands) a marginal additive in levels that wouldn’t impair the qualities of painting (whatever it is suspected to impair). The main difference between artist grade and student grade oil colours is something along the line of 50% more pigment and more pricey pigments, more than a few % of this thickener or other fillers to compensate. So to some extent colour strength wise, why not, but whether how much this increase is worth it is yours to judge.
My main concern for abuse of stearate (Al or Mg) is more in a risk of delamination. But if you’re painting on previous layers with reasonnable tooth, that’s not much of a risk. If you search for the topic on this forum you’ll find a few older discussions.
Aside for transparent colours that would be more likely to optically be affected by the presence of fillers, I doubt the difference would be that huge and thus worth the effort (and waste). Aluminium stearate is a white wax in pure form, but your few percent dissolved in linseed oil won’t pale it down much a,d doubt you can wash that much your colour.
I cannot say whether aluminium stearate would migrate through the soaking of the oil.
Oils are a lot of things, among which aluminium stearate is probably not the most prone to migrate in chromatography like that.

Without true IR or mass spectrometre analysis to compare, it’s only speculation that it goes.

I’d tend to think it’s mostly the free and smaller molecules of the oil that migrate, not the heavier and thickened, where I’d personally speculate it stays.

Might be actually more “sure” to dilute and mix a hundredfold your colour into pure oil, let it settle and then scoop the colourful sediment afterward, and filter pressure it. back to an oil colour. (surely even less worth the time spent on it, but possible)
Beside I don’t know what kind of contamination you get in exchange from the cardboard. Things migrate both ways, I’d be warry of that. For the video’s results, unfortunately one person’s testimony shouldn’t be taken as scientifict fact. So I won’t assess the colour strength results. Could be overstated or understated.
To this idea’s credit, this allows the artist to control the consistency and oil content in new ways, especially leaner ways against using mediums and reducing the colour strength.
So despite all I said above, I wouldn’t advise never to do that. 
I don’t think there’s much to gain but also there’s not much of a risk doing so technically (so long your cardboard/absorbant substrate doesn’t contaminate badly your oil). It might be a useful technique to the artist to control the oil content and consistency to some extent while keeping the pigment concentration high.
I’d still advise to use student grade paint for the ground and artist grade paint for the later details.
And not to mix brands so if something goes wrong, their support line can commit to help you safely. They can be shy about competitors products, they’ll be more commited to help if you’re “loyal”.
Cheers and good paint.
Lussh

Hello, Lussh,
I very much appreciate your detailed response.

What you expressed about the heavier contents, including the stearate, quite likely *not* being absorbed out of the student-grade paint and into the cardboard is exactly what I had suspicions about, given how the stearate gels.
Thank you for the following suggestion: 
“Might be actually more “sure” to dilute and mix a hundredfold your colour into pure oil, let it settle and then scoop the colourful sediment afterward, and filter pressure it. back to an oil colour. (surely even less worth the time spent on it, but possible).”
I would like to try this, however I couldn’t find any information on “filter pressuring,” and so I do not know what is meant by this. Could you suggest some resources or adjacent search terms that I can use to find out more on the “filter pressuring” process?
Thanks!

Hello there,

The filter pressure idea was just a thought exercise on how to remove more surely the stearate. I’m not aware of anyone doing that and wouldn’t see the point of doing so. 

I wouldn’t advise doing this when in my opinion your time would be better spent simply painting something with what you already have.

Nonetheless if you have that experimental spark, first you’d need a good whip or mixer to blend your colour and dilute in manifold in your chosen oil.

Then it would be like cheese or wine making, or any slurry that is pressed to separate strongly its liquid and solid parts in industry. In DIY I would try with some metallic grids in a kind of open piston​, add paper filters to the grids, and press the sludge in between by adding weight on top. So oil would pour in a container put below and you’d press your cake of oil colour between the grids.

Again, that part was purely theoretical. You don’t have to take my word for it.

Good painting and safe experimenting to you,
Lussh,