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For really high quality results, I find I have to make the focus increment very small. On my camera there is a "focus peaking" option that highlights the areas in focus. I use this to increment the focus so that the new area in focus overlaps with the old. I have sometimes ended up with a stack of over 50 images. In order to stack these properly in Photoshop you need to divide them into subsets of about 4-5 each. Blend those, and then blend the results of those in the same way. See for example, https://www.flickr.com/photos/stephenschiller/37210733816/in/dateposted-public/
Great project! I love taking obsolete technology and using to make working scientific instruments that would otherwise cost thousands.
You can buy plaster made especially for foundry work. it incorporates glass fibers and such. It may have slightly different composition as well. Adding sand may work nearly as well. But most DIY pottery stores sell silica at differnt mesh sizes that would work better as it will adhere to the plater better.
A small electric kiln (use for firing pottery) will work. I have one that accommodates about 7 by 8 by 8 inches that goes up to 2000 F, that I have used for mold burnout. (It can also be used for melting aluminum.) It also has programable heat ramps and hold times which is very handy as per the steps above. But it is small and I think it cost about $500. You would need something larger, and they make them larger, but more expensive too.
Alcohol is less toxic than iodine. Look up the lethal doses. Sounds like you are on a bit of an iodine mission here. Just because you take iodine every day below the level of toxicity doesn't necessarily mean it is good for you or anybody else. The body does need a very very small amount, micrograms per day, but not milligrams per day. And no, I am not a troll for the pharmaceutical industry. (That any such person would be following this tread so somewhat laughable.)
What do mean by "industrial ethanol"? Perhaps you are thinking of denatured alcohol? While denatured alcohol may be poisonous (depending on how it was denatured), it is very likely that the the ethanol in a tincture of iodine is NOT denatured. I say likely only because I don't know this for a fact but you can look at the ingredients on the label. If it says 5% ethanol it is not denatured. If it says 5% denatured alcohol it is. Furthermore, a few drops of 5% ethanol in a half gallon of water is totally safe, even for those who never drink.
Thanks a lot for posting this, my only complaint is that you never say what a ESP8266 is. (Of course I figured it out eventually). But for those of us not up on the latest part number buzz this would make your write up more complete