Making Valazquez medium for solvent-free oil painting

Chalk and oil paint in the wild, gamblin oil colour, 1980 student grade line.

https://gamblincolors.com/oil-painting/color/1980-oil-colors/

...In order to reduce the cost of oil colors, some manufacturers use gels and waxes to stiffen colors and replace traditional pigments with less expensive ones.

Our approach is different. 1980 colors are formulated with pure pigments, the finest refined linseed oil and marble dust (calcium carbonate). More affordable colors have been made with these three ingredients since oil painting began...

Emphasis mine.

I've a couple of tubes for art class as these dry faster than my M Graham studio paints.  I noticed the texture was more enjoyable for the 1980 paints than winton which is kind of weird to work with as all the colours behave the same (oil paint shouldn't as each pigment is chemically different).

as part of the glazing experiments I mixed up some limestone calcite with regular linseed oil to make a stiff putty and added them to a few of the underpaintings.  It was about 10% putty to paint.

This sped up drying time a bit and helped the transparent colours behave less slippery when painting.  But still kept the transparent nature of the paint.  

As I was doing the glazing about a week later, I didn't notice any difference in the experiments with calcite added and the ones without.  I suspect if it was sitting a long time between layers, like a few months, that the difference would be more noticeable.  

I opened the tube of my second batch of calcite, linseed, stand putty that had been lightly mulled and left in the tube for a couple of months...and had major binder separation problems. A big bunch of oil spewed out.

Don't know yet what to change to solve that.

But, it's really nice to mix with stiff paint to make 'long', especially cheaper whites.  It dulls the white down just a tiny bit and I can't help but wonder if this duller, longer paint behaves like lead white.

I don't like using my stand oil calcit putty for underpainting.

Yes, mixing with the white makes it nicer to work with and a touch transparent.   But it dries slower and shiny compared to no additive, due to the high amount of stand oil.

I think it's time to make a tube of underpainting like one of the previous mixes I tried where the black and white chicken dried too fast.

About 2:40, she mixes in some chalk to modify texture and drying time.

My second batch that I tubed started to separate and oooze oil everywhere.

That could be because I didn't mull it much.

Conclusion I draw from this is that if I'm not mulling, make it fresh just before use

from here

Extender Medium, previously called Impasto Medium, is essentially colorless paint made with inert pigments in linseed oil. It is intended to be used as the name implies, to extend paint. It is made from marble dust (calcium carbonate) and barium sulfate which are typically used as modifiers for oil paint to improve feel and dry time. When used in larger amounts, these pigments are categorized as fillers, as in the case of student-grade oil paints.

Extender Medium is a translucent, pale grey paste that has a similar consistency to most of our oil paints. It has a very low tinting strength and only slightly lightens and changes the sheen of most colors when mixed in. An ideal use for the extender Medium is when you want to mix a larger quantity of straight paint and don’t mind a slightly less saturated color or a muted sheen. Using mixtures made with Extender Medium can be a very cost effective way to cover a lot of surface area. Underpaintings are a great opportunity to use the Extender. It can also help mix certain tints and colors that would otherwise not be available simply with the addition of white or other tube colors. A normal brushed out layer dries in about 3-4 days.

Looks promising.

And pretty affordable at the local art shop