Solar Cooking Archive Discussion Forums

coconino · Joined: 21 Nov 2006 Posts: 77 Location: Sunny Brixton

Having read that research was needed regarding the practicality of blackening cooking vessels using oil, I bought some aluminium pots and experimented using linseed oil.

The cooking vessels I tried were cheap tiffin tins made in India and sold in Tooting, South London, for £3. Tiffin tins are available in many designs and in quality varying from lightweight aluminium to heavy-duty stainless steel. The latter are obviously much more expensive and I've seen them for as much as £18 for a three-tin set. I don't know how much they would cost in India.

Applying the oil to new tins proved problematic as the oil tended to clump and bead on the surface so I tried roughening the surface with wire wool (like a Brillo pad but without the soap) and then applying the oil using a cloth. This worked to some extent but there was still some beading of the oil so I next tried using fine grit sandpaper. I worked over the entire outside surface of the pots with the sandpaper, trying to get an even roughening right up to the edges and under the lip of the pot. Once this was done I wiped raw linseed oil over the outside of the pot and then held it over a gas flame (using a clamp to hold the pot), and turned it in the flame to try to get it heated evenly. This worked very well and the pot began darkening after a few minutes and I managed to get it to a good dark blackish brown.

Using another pot, I tried getting the oil sooty before heating over the gas. First the pot was roughened using sandpaper, then the oil was applied using a cloth, then a candle flame was applied to the pot in such a way as to generate sooty smoke. This looked very promising at first, creating a good matte black surface, but when the pot was heated in the gas flame the soot seemed to create patches which caught alight and left the coating uneven and patchy.

In both cases the resulting surface coating (once cooled) is robust and easily withstands light scrubbing and normal washing. In communities where water is scarce and people use sand or earth to clean their pots the coating may not last very long, but it can always be re-done.

While heating the coating, I found that it is important to keep the pot moving in the flame so that the heating is relatively even and the oil isn't allowed to catch light. It would be interesting to see whether a similar effect can be created using a kiln or by putting the oiled pots in a wood fire. When I attempted to bake the oiled metal in a gas oven the oil simply melted and ran off the sides of the pot, pooling on the drip tray.

In my experiments, the heating created discolouration in the bare metal inside, and also some oil adhered to the inside of the vessel and became blackened. I used wire wool to remove the worst of the unwanted blackening but the discolouration remained.

Lastly, I tried stripping off the coating back to bare metal using sandpaper and then I reapplied the oil and heated it again in the flame. This resulted in a smoother coating which was darker and more evenly black, though this could also be the result of my having had more practise at heating the vessel evenly.

coconino · Joined: 21 Nov 2006 Posts: 77 Location: Sunny Brixton

From my reading (I don't have the reference to hand, but it was in the SC archive) it seemed that there were properties in linseed oil which promoted blackening. When I get a chance I'll try other oils, perhaps mixing them as well. My thought about using a plain oil rather than a "product" as such was that it would be easier to obtain plain oils in remote places, though having said that I have no idea how widespread is the use of linseed oil.

I've recently gone to the other extreme and used Plasti-Kote woodstove spray on some jars and tins, but that's nasty stuff to use and although it's stuck well to the glass I'm not convinced it will last long on the metal.

coconino · Joined: 21 Nov 2006 Posts: 77 Location: Sunny Brixton

Regarding the Plasti-Kote, the manufacturer's web site has masses of technical information about their paints, and from this I learn that the woodstove and barbecue paints are identical.