So I did some more research and while a fresnel is used to melt metal, etc, I didn’t find any references for firing kilns. Makes me think it has something to do with the relatively small focus area. Uniform firing may be hard. Because hard to think that someone who melts metal with a Fresnel for keeda didn’t try baking clay at some point.
So, the parabolic mirror in the experimental design in my head has been replaced with a “tank” type structure made of brick. And we may possibly need a hybrid kiln, with the fresnel providing the temperatures, but some way to distribute them. This is a design challenge. Some ideas I am toying with:
- A brick enclosure with a raised platform for placing pottery (this is standard kiln stuff) and some kind of wood/kindling to create an overall fire? Might as well use a wood kiln.
- A brick enclosure with a raised platform with some kind of cover that gets heated by the fresnel and fires the contents by raising the temperature of the whole area covered by it.
- A brick enclosure with the ceramics buried in sand and heated with a slightly out of focus Fresnel covering a larger area. This could work, but the temperatures will need watching. Last thing we need is to fuse the sand and um… surround our greenware (unfired) ceramics in it. lol. Small broken pottery pieces may be a better idea but will probably not be as efficient unless quite small.
- Brick enclosure with out of focus Fresnel warming the whole thing, and a small amount of wood/paper/cowdung/whatever-is-handy-and-will-burn added in the end to “finish off” (we can evaluate if this is needed with experimentation)
I don’t have a clear answer yet, but a brick enclosure or some kind of structure that holds in the heat sounds essential if we are to use a fresnel (as opposed to say… chucking the greenware onto the coals of a campfire).
Doable hack. Instead of one large Fresnel lens, we use an array of smaller ones - each will have its own focal point (don’t think Fresnel lens can converge focal points, given that same source of light), so heat will be distributed. Make them all slightly off focus so they project squares rather than points of light, and we should be in business.
A good material to line the brick enclosure could be “ceramic fiber” - apparently it is used for insulation in indoor kilns. Though not sure we need an insulation beyond the bricks outdoors. Or heck, we can simply pile up mud into a box-like shape and it can fire itself in its own time from use
Thought of using some reflecting material for the heat on the inside, but it will likely melt so no point.