Fumed silica and Colloidal silica are different things.

I use Fumed Silica a lot, it’s great stuff and really easy to make, You don’t need to mull it either, just mix with a palette knife and tube it and you’re good. It was used by Langridge as a stabilizer in the past and there is no oil separation in the tube etc. You can also use it to shorten paints that are long if you make your own. I’m using it to reduce the strength of PW6 along with Calcium Carbonate, it works really well. It’s also a very good way to extend your paints, it’s virtually transparent and when added to paint you can see a distinct shift in color that I like. Look for a Gallon of it on Amazon, trade name Cab-o-Sil, it’s much cheaper than what naturalpigments is selling.

Note, there’s information out there that says it has a high oil content so it can’t be used for certain things. This is because it has an incredibly low density which makes it look like it contains a lot of oil ie by weight it’s ~140gms of oil to 100gms of fumed silica but the Critical Pigment Volume Concentration (CPVC) of Fumed Silica in linseed is ~94% which means that that oil content is very low, in fact it’s lower than any pigment you’re likely to have.

Also, I think fumed silica is considered a major inhalation irritant, so be careful if you experiment with it. Wear a mask!

Fumed silica is not a powder, it looks like a large “popcorn” looking agglomerate product in which micro-particles of silica forms ultra light weight giant agglomerates. It can’t give any dust and therefore safe to use. It can’t form dust. I used a lot of this product in chemical laboratory and never needed to use any dust mask. But Glass particles or dispersed quartzite can be an issue. When you are working with milled silica, then dust mask is necessary.

Just tried a little experiment with the West System 406 and some refined linseed oil (W&N, about 15 years old). It made a gel easily. At first, I tried 2.5ml of the silica in a little pile with a dimple in the middle, poured in 2.5ml of oil, and mixed with a knife. The result was very stiff and looked a bit grainy. I then added a little more oil – no more than 1ml (poured from the refilled 2.5ml measuring spoon), and mixed some more.

This resulted in a gel that felt pretty similar to artist grade oil paint…

[ATTACH]848750[/ATTACH]

I then squeezed out a little W&N French Ultramarine, and then took some of the gel and little bit of the paint…

[ATTACH]848751[/ATTACH]

The blade on the painting knife to the left is about 32mm long.

And mixed them together…

[ATTACH]848752[/ATTACH]

It felt a little stiffer than the ultramarine paint on its own, but only slightly, and it seemed to feel smooth and buttery under the knife when I spread it out. It certainly holds its shape in the main lump – I don’t get the impression that it would settle or level.

About the only reservation I have is that the West System 406 particles seem to be quite large, and either vary in size or tend to clump a little in the mix. A few larger bits can be seen in this closer view, especially to the top right…

[ATTACH]848753[/ATTACH]

Looking at the smear through a loupe, it does seem to have a slightly textured or reticulated look to it – particularly evident in the violet-leaning area in the middle. The area shown in the close-up photo is about 32mm wide.

The West System 406 does seem to clump a bit in the tub – scooping some out results in a combination of powdery stuff that seems to be loose particles, and small clumps a few millimetres wide that easily break up. I didn’t make any attempt to reduce it all to a powdery consistency, and the mixing time with the knife was just a few seconds. Perhaps putting the silica through a sieve would help, or maybe spending more time mixing it with the oil. Maybe mulling is what’s needed. (I have no idea how this compares to commercial versions.)

With regard to volume, adding the silica didn’t seem to make a noticeable difference. I didn’t measure the volume of gel before I starting playing with it, but looking at the two piles I ended up with (one clear, one blue), I’d say they’d manage to fill the 2.5ml spoon and no more.

Judging the stiffness with a such small quantity would be quite tricky by measuring out volumes of the components. To get a reliable recipe, it would have to be made in a larger quantity and the volumes carefully noted – the tiny bit of extra oil I poured out made a big difference. With the West System 406, the proportion by volume was about 55-60% oil to 45-40% silica.

In terms of extending the paint, it seemed very effective – the little bit of blue was probably about 15% of the volume of the bit of gel. When spread out, the result was a bit lighter than the raw paint, suggesting increased transparency. (The palette is white melamine, incidentally.)

Actually, you do need to wear a dust mask even when it is coffee powder form to keep it out of your lungs. Hope you know how dangerous coffee powder can be, when inhaled or when inhaled chronically.