My friend Mark brought me a pickle jar full of bright orange sludge that he scraped from a tunnel near Okugome Dam. He saw the color and thought I might like it. Yes, indeed!
And now I have a new earth pigment. I’m calling it Okugome Ochre.
It’s actually a lot more difficult to identify than I expected. Ochre, sienna, and umber are the main pigments formed from various ratios of iron oxides, clay, and sand. On top of those classics are myriad variations and similar pigments. It’s difficult to confirm exactly what I have without x-ray diffraction testing.
So I used physical characteristics and simple tests to try to figure it out.
- The rusty orange color indicated iron oxide.
- The sediment smelled like iron.
- It dissolved smoothly like clay does.
- It left a lasting orange mark on wood and tile.
- It’s magnetic. Considering the local geology, maybe goethite or limonite.
- It doesn’t react to acid, indicating iron oxide.
- A chemical test was hard to read because the iron stained the strip.
A day after collection, the sludge had separated into three layers: orange water at the top, then two layers of sediment. There were long strands of something in the middle layer sediment. I think they are iron oxidizing bacteria. Wikipedia explained it succinctly: iron bacteria convert dissolved iron into an insoluble reddish-brown gelatinous slime. That tracks.
This will make a nice pigment, even if it isn’t a classic ochre. I spent several days washing, filtering, drying, sieving, and grinding the sediment into powdered pigment.
But I’m not entirely done yet.
Japanese bengara is a traditional red iron oxide pigment that is heated to make it darker. I think there will be some experimenting with my Okugome Ochre to see if I can shift the color with heat. Oh, fun!
I’m glad to have friends who feed my obsession with natural color.
