Very cool spoon!
Casting in Green sand, Petrobond or (Delft) clay is indeed less suited for detail and a smooth surface finish. And cumbersome with regard to finish, but a great entry point for casting.
Will say Delft Clay is best of choice in my experience, more oil in the substance, better cohesion and clearance of model.
Air venting en flow of silver is where we learned the most. Also, heating the clay a bit before pouring seemed to help (but not to much, because of the release of oil when heating).
Have tried a couple of models with detail, but best do detail with lost wax as you mentioned.
We have been playing with Braluminium, alloy of bronze and aluminium. While not suited for collectibles, nor precious, good stuff!
Thanks for the inspirational post and valuable comments of others.
Maybe a Pyrite version of the spoon for BCH? (though Pyrite is brittle, and toxic when heated)
I use Petrobond for less expensive metals like copper and brass when I have the patience to hand finish things or lose detail. I've never used Delft Clay because of the cost. Do you bother cutting vent holes when you use delf clay/green scand/ or petrobond? Ive had pretty decent luck just using the porosity of the material itself. What I really do not like about the sand casting methods, is 3D models with lettering are realllllly inconsistent if you do any sort of lettering or detail where you can break the sand and remove features when removing the model. I had issues where if I applied inconsistent pressure when packing, sometimes I could remove the 3D model, sometimes I couldn't, etc. If I pack too hard vs not hard enough even if I didn't break features off, I'd get inconsistent weights as well which is really tough with this crowd.
I've not used pyrite before, but I'll look into it. I primarily use gold, electrum, argentium silver, fine silver, aluminum bronzes, copper, aluminum, platinum/palladium (though I need to retool to do those better) though I've tried a few exotics with mixed results. Purple gold is by far my favorite but the strangest material I've ever worked with. Its super pretty but has trash mechanical properties. This is a stock photo from google pictures, as I don't have any pictures of what I've made with it handy.
The primary method I use now is lost wax casting. I've got a Resin 3D printer which is slow as hell but produces unbelievable detail down to a couple of microns. I can buy castable resin for it and go straight from print to mold, but the resin is something like $375 per liter, so I just use the standard stuff that'll provide me with a good finish, and put it in a silicone mold so I can wax inject replicas. Material cost is still sort of ridiculously high for low batch things, but its a lot better than adding up all of the man hours that goes into making things individually.
With the spoon and about 50 other plans I have, the issue I am running into is my furnace size for burning out the molds. Its taken forever but I'm finally getting around to finishing up my 13.5x13.5x13.5 inch kiln. Ive just gotta make some finishing touches and install the electronic controls at this point and I should be all set.
-snap-
I did see refractory concrete breaks up after water vaporizes most of the times, I did see some nice molds of that concrete that done pretty well tho maybe making the mixture properly and the brand you use influences but that takes a bit of trial and default i guess.
On the other hand it can't be more than two days that I discovered stone for this purpose, however in past experiences with stone and fire stone can break up and no idea how'd I could carve there.
Thanks a lot for the encouragement, should of answered way earlier but even looking specificaly for this thread I saw nothing in new replies.
Plaster casts are typically 1 time use, but they give the best detail. Commercial products have all sorts of chemical additives to eliminate air bubbles, (though you still need a vacuum chamber) surfactants to keep the surface of the molds super smooth and without pores otherwise you get pits in your cast, and low shrinkage factors. DIY methods will work if you are careful and do a carefully controlled heat cycle to remove ALL moisture from the mold, but often the size of what you cast will be inconsistent at the very least.
I use commercial investment powders, and while expensive, give expected results more often than not once you deal with a few minor tweaks that you'll need to do regardless of mold material. The burnout cycles are provided by manufacturers, and typically take anywhere from 10 to 18 hours with VERY specific temperature heat soak/ramp schedules. They might require you start at 275 degrees (Fahrenheit) for 45 minutes, ramp up to 350 for 30 minutes, then up to 475 for 15 minutes, 550 for 2 hours, 675 for 3 hours, 900 for 2 hours, 1150 for 2 hours, 1350 for 1 hour, and then back down to 900 before you cast the material. Little things like not following the very particular timing/length can completely ruin an otherwise perfect mold. DIY products don't have manufacturer suggested times, so just know you'll have to do a bit of experimentation before you get it right.
Going to make this post even longer and just throw in a few pictures of things I'm working on.
And to physically hurt the bullion collectors here
