Originally Posted by tidal
.It is not however apparently very thixotropic according to my research but I guess experimentation is the name of the game
The terms Pseudoplastic and Thixotropic kind of confuse me and are often used incorrectly, so I am going to ignore any terms and just describe how a gel made with linseed oil and fumed silica behaves with a knife or brush compared to a putty or gel made with various types of calcium carbonate. I found just the opposite of your statement above, as far as achieving the type of gel I wanted with linseed and walnut oil. Additionally from my research, fumed silica appears to be the number one choice for getting a non sagging / non self leveling liquid in non "art" areas, particularly with epoxy resins - those talking about it use the term thixotropic to describe what it does.
What I want is a gel that is very easy to manipulate but not flowing / self leveling like maple syrup. I want it to hold sharp edges and peaks created with a palette knife, the same, plus brush marks when using a bristle brush. Once created, I want the shapes to stay as close to the way they look once executed without moving, softening, leveling, running. Nothing I have tried gives that better than fumed silica and oil.
Though I have not tried any real chalk dust, I have tried other fillers made from calcium carbonate. I am guessing that the reason chalk apparently behaves differently than ground calcium carbonate is because the particles are more like fumed silica. I found it impossible to create a gel that behaves that way with those fillers at any ratio using any type of oil. When enough filler was added to make it keep its shape, it became much too stiff to respond easily to a brush or palette knife. When thin enough to brush / knife easily, it became too self leveling, losing all the nifty textures I created, slumping down into a smooth puddle. I also found that adding any type of alkyd resin / medium to the gel made it self leveling / slumping, so the only dryer I add to mine when needed is CoZiCa or some similar metallic dryer, which did not destroy the nature of the gel if t was added while mixing in the fumed silica. If you add some dryier after reaching the perfect state, it can make it too runny, forcing you to add more fumed silica to balance out the added liquid.
A fumed silica gel does shrink more than a putty heavily filled with calcium carbonate, so don't expect to be able to build up 1/4" and thicker surfaces with it. It is best suited to lower height strokes. There are probably better materials to use than oil based gels or putties for thick applications. You could add oil paint on top of the sculpted surfaces to get the more appealing look of oil paint that you want.
FYI, Glass Microspheres
might be a better choice if you want to sand it. One page said that fumed silica is not a good choice to use if you plan to sand it down.
Maybe your perfect gel could be made using a combination of two more materials such as fumed silica and glass microspheres, or maybe fumed silica and calcium carbonate, all three or some other combinations entirely.