ROUGH sand casting test

[Will McGowan]

I'm a newbie trying the sand-cast and blow technique for the first time. My pieces came out with little grains of sand still attached all around them. I brushed the pieces like a maniac with a steel wire brush while they were still hot on the blowpipe and had used the olivine/bentonite/corn starch mixture that is suggested in Glass Notes with a generous coating of carbon from the torch. After they had annealed I tried soaking and scrubbing and the dremel and more scrubbing to no avail. Is this the way pieces stay when doing any sand casting or am I just off somewhere. I did let the pieces sit and cool awhile in the sand impression and thought maybe that may have been too much heat built up in the mold but was hoping some of you with experience could point out some mistakes and suggestions. Thanks.

[Michael Mortara]

3-4% Bentonite
3-5% Corn Meal
80 Grit Silica Sand

This is our sand casting mix, works like a charm.

[Will McGowan]

I think that is the fix! My grit is too small. Had to buy the closest that was available. I'll find some 80 grit and retry everything.

[Kenny Pieper]

Mike whats with the corn meal. Does that creat a carbon layer for a realease.


At Penland we use to use 1/2 80 grit sand and 1/2 180 or so along with 7% bentonite. The large sand gave the mold structure and the smaller size would fill in the gaps to give a smother texture. The bentonite makes the whole thing stick together. Proper amount of water is very important. Too little and the whole thing gets crumbly and too much and the steam will bubble up through the glass.

[Michael Mortara]

Corn meal is the release agent, it forms a carbon layer and makes your shop smell like a tortilla factory at the same time. We used to do a matrix of 80/100 grit silica but got lazy and just use the 80 grit now. Very clean castings, learned that trick at Pilchuck.

[Scott Novota]

So what is the quick short list of the process?


mix up the stuff.

Make the mold.

pour in the glass.

Set mould/glass in lehr? or Pull it out and just set the cast in the lehr? Sand blast it at the end?

Just wondering never done a casting.


Scott.
.

[Jordan Kube]

Originally posted by Michael Mortara
learned that trick at Pilchuck.

And every session the next instructor comes and does something different. The corn meal can go rancid. The worst thing I saw was using the sand once and then throwing it out.

[Allan Gott]

Originally posted by Will McGowan
My grit is too small.
I wouldn't say that at all. You have a release problem.

No disrespect to HH. I'd lose the starch. 5-8% Bentonite by weight with any sand. When you think you have enough acetylene carbon in the mold, do it again.

Graphite spray is a good release agent as well, either the Renite product($$$) or the stuff you can buy at hardware stores(not so much $$$). I use it in combo with the acetylene.

I would recommend keeping your sand as dry as possible. It's got to hold the impressions but be "fluffy" enough for the interior surface to dry when it's hit with the torch........and you gotta make a good shot going in.

Stating the obvious.....one shot to clean it, that's it. Any sand left on the surface is a design feature.

This is a trial and error process but once you figure sandcasting out it's kinda fun.

Good luck.

[Will McGowan]

I'm mixing another batch this weekend so I'll try it without the starch and see what happens. I thought about the graphite dust but didn't figure it would stick to the side walls since most of molds are pretty vertical. I didn’t know it came in a spray though. I was thinking I could make the mold before hand while the sand was still pretty damp and allow them to dry out all day in the sun. Didn’t know if that was a good idea or not.

Scott- Pretty much the right process. I’ve been molding them so that a fresh gather is dropped into the sand mold and blown just a bit to fill any gaps. Then I pull the piece out once it has set up a bit and go ahead and work it like a normal piece after cleaning off clinging sand. I’m sure there are many different ways of doing it though, like just casting a foot or leaving the piece as it comes out. I think the hardest part is getting the sand damp enough to keep its shape but dry enough not to bubble (hence the premade mold idea). I guess if you’re good you might get more than one use out of a mold but for me it’s just a quick one time mold.

[David Patchen]

Anyone ever use plaster as a mold for pours like sand casting? I'd think that if it was sufficiently dry it might hold detail well. Maybe it can't be prevented from sticking...?

[Wes Hunting]

We have been pouring into a 50/50 mix of plaster and fine silica (potters flint ) for a few years now with great results. The trick is to slowly bring the mold up to 1500 then bring it down to 1200 when your ready to pour. Then bring the mold back up to 1600 to get rid of any bubbles. This is all done in a roll out oven we built for the work. I was told by alot of people that you cant do this but I never listen.
If you hate rancid corn stench try lightly spraying your sand mold with a H2O and sugar solution, this also works as a good release.

Rancid Corn Stench = RCS
I like this term and plan on using it alot today.

[Allan Gott]

Yeah, it's a lubrication product Will. Comes in an aerosol can.

I'll guess from your last post that you have your casting sand way too wet. There shouldn't be the slightest concern about bubbling. This goes for ladle casting solid stuff too.

Can't give you a mixing ratio. I was taught to do it by feel and have never measured.

Another step that really helps is to run your damp mold mix through a coarse screen as you transfer it into the mold box/pail/whatever. This introduction of air to the mix has all kinds of good karma attached to it.

Ooooooommmmm.

[Greg Vriethoff]

Originally posted by Wes Hunting
try lightly spraying your sand mold with a H2O and sugar solution, this also works as a good release.

I have had good results with this as well. I like to use molasses (http://en.wikipedia.org/wiki/The_Boston_Molasses_Disaster). Mix it 50/50 with water in a spray bottle. Mixes easier than sugar, is better for your lungs than all that nasty soot from the torch, and makes the shop smell like cookies (albeit burnt ones :D ). Just don't overdo it. You'll have outgassing problems if you lay it on too thick.

[Matt Bezark]

that's a very interesting process!

i looked at your website. great work! the bike's nice too.

do you have any images of work made with this casting technique that you can share with us?

thanks,

matt.

Originally posted by Wes Hunting
We have been pouring into a 50/50 mix of plaster and fine silica (potters flint ) for a few years now with great results. The trick is to slowly bring the mold up to 1500 then bring it down to 1200 when your ready to pour. Then bring the mold back up to 1600 to get rid of any bubbles. This is all done in a roll out oven we built for the work. I was told by alot of people that you cant do this but I never listen.
If you hate rancid corn stench try lightly spraying your sand mold with a H2O and sugar solution, this also works as a good release.

Rancid Corn Stench = RCS
I like this term and plan on using it alot today.

[Dave Bross]

Matt,

All of us here on the southern sandbar (FL) were looking forward to you and your work coming here so we could see it and pick your brain. Looks like that must be on everlasting hold so would you share what you're up to technique-wise?