This is another obsessive project where I spend an unreasonable amount of effort trying to capture a particular look for a prop. In this case, I wanted to duplicate the appearance of a fired clay idol that had been buried underground for a long time.
I'm certainly not the first person who's tried to duplicate the patina of an excavated artifact. In fact, reproducing the combination of dirt and soluble salts that accumulates on those items has been a favorite of forgers for centuries. Get the patina right and you can turn a 2 piastre clay figure from the souvenir stands of Cairo into a genuine archaeological find worth considerably more to a gullible tourist.
Unfortunately, I couldn't use the traditional approach of placing the "artifact" in the water tank of a toilet and waiting for the whitish haze of lime and salts to develop naturally. That process takes months, although the results will pass even close inspection. Worse, my material of choice was cold porcelain clay. When dry it does an excellent job of duplicating the mass and hardness of real clay, but it's considerably easier to work with. It's also water soluble, which means exposing it to water once it's dry will just turn it back into a malleable lump of PVA and cornstarch again.
That meant the patina had to be a combination of surface texture and a convincing paintjob. Sculpting the actual idol went relatively quickly. I wanted something primitive, but not too crude. There had to be a certain refinement to the lines of the piece. I eventually settled on a shape that looked like a ball on top of a curved cone. I wanted to have as few features as possible so that it could pass as an odd skull fetish or maybe a decorated hand tool. At the same time there had to be enough detail that someone familiar with the Mythos would recognize it as far more than a glorified hammerstone or pestle.
Here's the final result. I'm skipping the entire sculpting process, mostly because it looked terrible right up until I applied the final paint job. It probably didn't help that I tinted the clay a dark reddish-brown, so it looked uncomfortably like a lump of...well, something unpleasant.
A view from the right. Building up the texture of the encrustations was a two step process. On the first pass I stippled the entire surface with paper clay thinned down to the consistency of heavy cream. The second application was a spot application using a thick, intentionally lumpy mixture. The entire piece is about six inches long.
This shot gives a better look at the contrast between the terracotta base surface and the patina treatment. I wanted the reddish brown "clay" of the idol to peek through the accumulated salts and lime.
The patina buildup is heaviest on the face area of the figure, but the eye sockets only have a light layer of calcium haze. That seemed to make sense if the idol had been dropped and then buried. The weight of the head would have positioned the idol face down and tilted at an angle, leading to more buildup on the lower surface.
Click through on this shot to get a good look at how the final paint treatment came out. The base coat was a thin layer of terracotta over the existing red/brown surface of the idol. On top of that I did a wash of thinned white paint to produce the hazing effect, followed by drybrushing with burnt umber, light tan, and a touch of white.
All in all things turned out pretty well. The result looks convincing, but the patina buildup may be a bit heavy. I should knock it back with a light wash of terracotta. What I found interesting is that this style of patina is applied exactly the opposite way of a normal finish. Normally you start with a dark basecoat and apply increasingly lighter highlight layers. In this case the dusty appearance comes from starting with a midtone base and then a pure white wash, followed by a darker layer of burnt umber and a light drybrushing.