..oh, and I did say "BIO" chemistry.

I assume the EPA is more concerned with protecting endangered species of pond slime that the actual water chemistry.

Of course, that's an ASS U M PTION...
:roll:

Fine, I'll dump it in the trash, right next to my oil fliters....

FYI...

http://www.canyonstatedentalsupply.com/garreco2.htm

Don't know whether they sell to non-dentists or not, I just ordered a 50# box from Clint Sales, and was looking for something else.

Don't know about shipping, either...

No, I've just worked in a lot of fabrication related jobs.  Etching glass, reproducing architectural features (like antique plaster trim on Victorian era houses) and stuff like that.  I've also done a lot of pottery, including slush casting with slip clay.  About 5 or 6 years ago, I also was involved in a start up company to sell wargames terrain online but we lost our first round of finished product in a shipping accident and neither myself nor my business partner had the money at the time to start again (refunding preorders sucks).  As well, since then the USD has really dropped and shipping costs from Canada to the US have doubled, so I don't feel so bad about that anymore-- we couldn't operate in today's environment as the US was our target market.  I'm also an information sponge kind of a thinker, so things like the fact that resin shrinks but plaster expands stick with me.  :shock:

My Excaliber arrived today!

Frankly, it's not real exciting to look at - it's just an enormous clear plastic bag of light gray powder at this point. It's about half a cubic foot - volume wise - for 50 pounds.

I'll use my crappy kitty litter mold tomorrow (if it doesn't rain) and see how hard it is and just how much volume it looses when mixed.

If it rains, I'll cobble up a starship model to make a mold of.

Well, the models are at home, and they hadn't dried enough to throw, but I de-molded them after about 30-40 minutes. I mixed WAY too much, so I dumped it into a old meat container I had purloined for just this purpose. The WASTE from the process seemed to be as much a pint of resin would fill.

If the plaster is good enough for most models, then it's WAY more cost-effective - despite my previous reservations. Not to mention less mess and no noxious-ness....

I think even with slush/rotational casting with the resin, the excaliber will probably be quite a bargain.  Add in the longer mould life and the lack of noxious organic solvents and you may find yourself looking at resin as being the situational thing you'll grab only for certain models and mould types.

I'm contemplating getting some dental stone specifically made for rotational/slush casting.  Stuff that sets up quickly.  The dental supply place that's relatively local to me said they had some.  They said they have customers who are artists who buy the stuff to do hand rotational casting where the person turns the mould around by hand.  I love the sound of cheap, mostly hollow, strong gypsum casts at a low cost.  They also said that it'll work as a regular (albeit quick setting) casting stone. 

I'm hoping I can get dental stone to work in a two part mould.  I've never tried it.  I've only ever done a single sided cast with the stuff.

Well, I just put some water in a throwaway cup (less than 1/2 cup) and put in as much plaster as it looked like it would hold.

Hirst Arts basically said mix this like you would plaster, the ratio wasn't critical.

Next time, I'll use less water to start out with.

I used to add a decent amount of black acrylic paint to the water (the cheap stuff from the dollar store).  It was more for terrain stuff-- I wanted any part that chipped not to be glaringly white.  Worked quite well.   I didn't notice any change to the final pieces beyond colour.  Some people claim adding like 5-10% of the volume of the water in white glue gives the pieces a smoother finish and makes them more resistant to snapping.  There are also polymer additives for gypsum based cements you can get, but I don't know anything about those.

I looked a bit more into admixtures.  I see what they're for now.  They should work marvelously with any gypsum based product.  Though with the break strength of excaliber on it's own, I can see why you might not bother.  Does the piece with the admixture have to cure overnight in the mold, or do you demold it first?

So, Jim, you done anymore with that Excalibur, or is it too damn cold to do anything there too?

Sorry about posting to an old thread.  I figured the forum isn't fast paced enough for it to be a huge issue.

I've been making moulds of stuff I built and casting them with gypsum based putties for the last year and a bit.

I eventually settled on using silicone sealant, thinned with silicone oil (a non toxic alternative to naptha and easily available as it's used to put inside of shocks for RC cars), the curing accelerated with cheap acrylic craft paint.  The moulds are flexible and strong and I've cast them all atleast 10 times and they haven't degraded.

I'm finding the dental stone stuff easier to work with than resin.  I've been building my masters to be cast as one sided moulds, but have even had some luck making two part moulds and pouring them, plugging them and hand rotating for a slush cast.

I'll see if I can borrow a friend's digital camera, but sadly I don't have one right now.