I have a long, fairly narrow mold where I would like to place a color frit into the deepest areas and then drip cast a differing color in for a more translucent appearance in the body of the casting.
Has anyone done this and what are the visual results?
Thanks
Placing Frit + Drip Casting into Same Mold?
Moderator: Brad Walker
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Gale aka artistefem
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charlie holden
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What happens is that the glass wants to be the same depth across its surface when it is hot, but there is more pressure to spread where it is deepest. The deepest point is right under the drip, where there is a pile of soft glass. All the glass under the drip is trying to spread out, except right against the bottom of the mold where friction is very high. So the top surface of a spreading drip moves fastest, but almost all of the glass is moving some.
When you drip glass into a deep, open faced mold it piles up under the drip and spreads out in a circle, with the leading edge of the mass being about 1/4 inch deep. When the leading edge encounters some resistance, either a mold wall or some more glass, it stops spreading and starts to deepen. The deeper glass behind it, still pushing out, moves a little faster on its top surface, but still moves through its entire depth. If that drip continues to be fed and gets deeper than another mass of glass it has run into, it will push most of that mass in front of it, so that both masses of glass are getting deeper.
Lets say you want the frit to be the only kind of glass in that section of the casting and the dripped glass to fill up the rest of the casting. This is for a pieces that is more than 1/4 inch thick in all areas, with a flat bottom. You have to fill the frit section with a pretty high mound of glass. The frit will consolidate and start to spread before the dripped glass spreads far enough to push back much. At first the frit is much deeper than the leading edge of the drip. So the frit will push into the area where you want the dripped glass to fill. Eventually the dripped glass will get deep enough to push back against the frit, but it will push mostly against the top surface. So you end up with frit glass bulging into the dripped glass, underneath dripped glass bulging back into the frit glass. The border between the two masses of glass will be sloped.
If you want the frit glass to fill in a low area and the dripped glass to cover over the top, the frit has to be in low, narrow depressions. Otherwise the drip will push the frit in front of it as it spreads.
Two drips of exactly the same weight placed centered in two halves of a flat bottomed, open faced mold will form an almost perfectly straight line where they meet. That's because equal masses of the same depth meet in the center of the mold and spread equally towards the edges. But any imbalance will give you some kind of curved interface where one mass of glass has spread more quickly into an area than the other.
ch
When you drip glass into a deep, open faced mold it piles up under the drip and spreads out in a circle, with the leading edge of the mass being about 1/4 inch deep. When the leading edge encounters some resistance, either a mold wall or some more glass, it stops spreading and starts to deepen. The deeper glass behind it, still pushing out, moves a little faster on its top surface, but still moves through its entire depth. If that drip continues to be fed and gets deeper than another mass of glass it has run into, it will push most of that mass in front of it, so that both masses of glass are getting deeper.
Lets say you want the frit to be the only kind of glass in that section of the casting and the dripped glass to fill up the rest of the casting. This is for a pieces that is more than 1/4 inch thick in all areas, with a flat bottom. You have to fill the frit section with a pretty high mound of glass. The frit will consolidate and start to spread before the dripped glass spreads far enough to push back much. At first the frit is much deeper than the leading edge of the drip. So the frit will push into the area where you want the dripped glass to fill. Eventually the dripped glass will get deep enough to push back against the frit, but it will push mostly against the top surface. So you end up with frit glass bulging into the dripped glass, underneath dripped glass bulging back into the frit glass. The border between the two masses of glass will be sloped.
If you want the frit glass to fill in a low area and the dripped glass to cover over the top, the frit has to be in low, narrow depressions. Otherwise the drip will push the frit in front of it as it spreads.
Two drips of exactly the same weight placed centered in two halves of a flat bottomed, open faced mold will form an almost perfectly straight line where they meet. That's because equal masses of the same depth meet in the center of the mold and spread equally towards the edges. But any imbalance will give you some kind of curved interface where one mass of glass has spread more quickly into an area than the other.
ch
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Gale aka artistefem
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Excellent info.....thanks!
Getting exact color placement into this mold shape is proving to be a bit of a holy grail. Looks like I'll have to make a two part mold and lay up the colors in a pate`method, leaving sprues along one edge to finish the filling process. Even with this approach, the colors can slip around as the mold fills. I seem to be at my kiln god-er's mercy on this one.
Gack! Stretching one's knowledge and abilities is good, right????
Getting exact color placement into this mold shape is proving to be a bit of a holy grail. Looks like I'll have to make a two part mold and lay up the colors in a pate`method, leaving sprues along one edge to finish the filling process. Even with this approach, the colors can slip around as the mold fills. I seem to be at my kiln god-er's mercy on this one.
Gack! Stretching one's knowledge and abilities is good, right????
I don't notice you are talking about dripping into a mould Gale, I thought you were dripping it direct into something like a plate mould.
You probably know about this already, but I found that by putting a good solid chunk of glass into the bottom of the clay flower pot, covering the outlet, seems to get the glass into a good pouring consistency and it seems to whoosh/gush out quickly, is the best way I can explain it.
.
You probably know about this already, but I found that by putting a good solid chunk of glass into the bottom of the clay flower pot, covering the outlet, seems to get the glass into a good pouring consistency and it seems to whoosh/gush out quickly, is the best way I can explain it.
.
It ain't where you're from, it's where you're at!
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Gale aka artistefem
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Paul....my original question did ask about the possibilities of dripping onto frit. Based on the replies to this question, it seems this won't work for me.
The mold is fully 3d & enclosed, rather than open faced. I need to retain my color placements in several areas located along one long length of the glass piece.
Making a 2 part mold with specific color placement may be my only option. I'm afraid if I try to do a drip the colors will move around too much, flowing with the glass movement created by the drip.
The mold is fully 3d & enclosed, rather than open faced. I need to retain my color placements in several areas located along one long length of the glass piece.
Making a 2 part mold with specific color placement may be my only option. I'm afraid if I try to do a drip the colors will move around too much, flowing with the glass movement created by the drip.
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Lauri Levanto
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What Charlie said is a good part of the story. I had never thought the role of hydraulic pressurein such detail.
There are counter measures, however. You place the first
color frit where you need it. Then you add secind color frit on top. As charlie said more close to the mold surface friction
reduces movement and it is the secind color that moves.
Bubbles are a concern. Deep mold of an insulating material
keeps ypur frit cool longer. The pot melt -especuially if you have top elements, melts first and is glazing over frit. This seals air into the lower part.
In one frit cast case I wanted clear on the deepest part
of the mold and blue on the top. The clear I had was very fine and the blue was coarse. The darker blue absorbed heat faster, melting first. The clear below conteined so much trapped air that when it melted, it has a smaller specific weight andfloated up.
The subject was a clear figure, swimming in blue sea.
What I got out of the kiln was a blue swimmer in a clear sea.
If you use a pot with a large hole, the sinking column of
soft glass has more pressure and tends to fall deeper into the molten frit. With a small hole and higher temp,
the dropping glass is more fluid and levels better on top of
the frit molten part.
-lauri
There are counter measures, however. You place the first
color frit where you need it. Then you add secind color frit on top. As charlie said more close to the mold surface friction
reduces movement and it is the secind color that moves.
Bubbles are a concern. Deep mold of an insulating material
keeps ypur frit cool longer. The pot melt -especuially if you have top elements, melts first and is glazing over frit. This seals air into the lower part.
In one frit cast case I wanted clear on the deepest part
of the mold and blue on the top. The clear I had was very fine and the blue was coarse. The darker blue absorbed heat faster, melting first. The clear below conteined so much trapped air that when it melted, it has a smaller specific weight andfloated up.
The subject was a clear figure, swimming in blue sea.
What I got out of the kiln was a blue swimmer in a clear sea.
If you use a pot with a large hole, the sinking column of
soft glass has more pressure and tends to fall deeper into the molten frit. With a small hole and higher temp,
the dropping glass is more fluid and levels better on top of
the frit molten part.
-lauri