Drip casting crucible placement

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Ron Coleman
Posts: 468
Joined: Sun Mar 09, 2003 3:20 pm
Location: Columbus, Ohio USA

Drip casting crucible placement

Post by Ron Coleman »

I finished another drip casting today and as I watched the glass flow from the bottom of the crucible (flower pot) I was wondering if there is a "best" location for the glass stream to enter the mold. This casting is a hollow core vase about 7 inches tall and the glass was entering centered on the rounded end of the core and then flowing down the sides. The pot was about three inches above the point of impact. Casting temperature was 1750 f, BE glass with a plaster/silica/fiberglas mold.


Also curious if the hole diameter in the pot should be altered for faster glass flow. The 4 inch post I'm using have about a 3/8 inch hole.
Ron
Steph Mader
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Location: Freeland, WA
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Post by Steph Mader »

Hi Ron,

3" is about where I place the pot, too. I put a couple long kiln posts in a V shape, and put the pot on top. The higher up the pot is, the more movement in the glass stream. If it's around 5" or so above the mold, the bottom of the stream starts to drop in a circular motion. I wonder if that would minimize the trapped bubbles you wrote about earlier.

I'm casting with Lenox lead crystal and taking the temp up to 1550. The regular hole in the pot works fine at that temp, emptying in 3- 4 hours or so once it gets going. I'm holding at melt temp 6-10 hours, to let the larger bubbles make their way to the surface.

At 1750 I'd be concerned that the mold would be breaking down badly. 1550 is even pretty tough on them, especially if it's a big piece with lots of glass weight bearing down on it. I think Lani mentioned to me that they were casting Bullseye at 1550, and you would probably get less flashing.

That's my bit.
Steph
watershed
Posts: 166
Joined: Wed Mar 12, 2003 1:44 am

Post by watershed »

I'm with Steph on the set up. But I have taken to drilling more holes in the pots. I go for 3 total. But I'm also trying to push 25lbs of glass through it. My logic is more holes = less resistance to flow= flow at lower temps= faster firings.

That's my story and I'm sticking to it.

Greg
charlie holden
Posts: 260
Joined: Thu Mar 13, 2003 8:26 pm
Location: Atlanta

Post by charlie holden »

I think it's all mostly up to you. In general, the smaller the hole and the higher the glass falls before it hits the mold, the more color mixing you're going to have. Smaller holes lead to thinner lines of color. More height leads to more looping of the glass as it pools = more lines of color. If you get way up there, (6 or more inches), the glass loops wildly and you'll get more of a cloud of color rather than distinct loops in neat circles.

You can enlarge the holes with a hacksaw blade or a jigsaw on low speed or a round file. I sometimes cut mine into slits so that the glass flows out in a ribbon rather than a cylinder. It folds back and forth on itself and you can keep the colors at each end of the slit apart from each other.

1700 is hot for molds but if they are staying together, why worry? Remember, someone casting lead crystal is putting 50% more mass per volume in their mold than someone casting soda lime.
Jerry

Pot melts

Post by Jerry »

I use your system Ron and usually have no trouble with it. I wasn't going to tell this story on this board because I just know how much grief I'm going to get, but you've asked and this relates to your question.

Two nights ago I did a pot melt into a cup about the same size as the one you described. I was usuing Spectrum transparents with the pot about 3" above the gate. The only difference was I had used this pot before to do a melt dirrectly on the kiln shelf and had already modified it to a larger hole about 3" long and 1" wide. Well, when the glass began to flow it really did flow; too fast to go into the mold. It overflowed all over the mold down the sides and all over the shelf with almost none actually inside the mold. Wot a Mess.

The rest of what you do is what I've always done successfully so, IMHO you should stay with it.

Jerry
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