Flaw in BE glass shows as defect in blank - how to fix?

[seachange]

Hi

Have fused a round small plate 1/8" tekta on the bottom, 1/8" egyptian blue on top, to full fuse.

Beautiful, except for where there was a sort of 'scar' on the egyptian blue. This imperfect area has now left a distinctive trail of bubbles on an otherwise almost bubble free blank. Because the bubbles are concentrated along a 1 1/2" line, it looks like a defect.

The blank is now in the kiln again, with a light dusting of crystal clear powder, to see if this improves the surface.

Have 2 questions:

Am a bit confused about the comment in "BE Quick Tip : fix surface flows". It says that - compared with overglazes - the clear powder "fires quickly". Does this refer to the top temperature, that one does not need to go to a full fuse? The tip recommends refiring at 1425-1450F. My full fuse fire is ready at 1490F (slow bubble squeeze firing).

The blank is 7" diameter (am optimistically planning for bigger ones ). Since it is the second fusing, I understand that I have to slow down the ramp rate, therefore not sure how to "fire quickly".

Second question is about the scars and other marks on the glass. Because of transport issues I have to buy the glass in pre-cut sizes and live with what arrives in the box.

I understand the problems of hand manufacturing and like BE glass not only for its color range, but specially for its commitment to the glass community, therefore would like to find someway to deal with the flaws.

How do you work around this?

Thought that I should perhaps sprinkle a layer of clear powder on each blank, as a prevention method...is this a sensible approach? It would save an extra firing, but don't know if this is the best way.

Hope you'll share your method with me, it is amazing how many things one has to learn when working with larger pieces. With the help of this board, I am slowly getting there.

Many thanks for your insights, seachange

[Morganica]

I have absolutely no idea what they mean by "fires quickly," unless they mean it melts fast so you don't need much hold time to mature the surface. You need less heatwork to melt powder into the surface than to soften the whole thing, but I'm not sure how that saves all that much time--you still have to ramp up and anneal. Maybe someone from Bullseye will chime in.

The surface flaws they're talking about, though, are mostly devit and other very shallow things. If you can see/feel a change in depth with the flaw, a light coating of powder may not do much more than make the hole shiny.

If the flaw is trailing bubbles, it's more likely a dip in the glass that trapped air, from the handmade glass. You get around that by prefiring the sheet before you use it in your composition. That flattens the surface and makes it less likely to trap air.

[seachange]

Hi Morganica.

Tried to take a picture of a flaw in the glass (before it is fired - on another piece) but it doesn't show up.

The defective area, before firing, looks a bit like someone had slid a finger on the glass, leaving little curves close to each other, similar to when one uses ink to make a fingerprint.

This flaw seems to be very common in BE glass. I find it often in 2mm dichroic glass, and have learned to cut around it, because in that area the dichroic coating often breaks up a bit, showing the black base, and ruins the piece. This is easy to do for jewelry, with big pieces things get more complicated .

To make sure I understand this correctly: in these plates the opal glass is on top of the tekta, on the air side (I am using the tekta underneath the opal only to get to 1/4" thickness, for a more robust plate).

After a full fuse, the defective area on the top, uncapped opal, changes to a trail of bubbles (the air must have been trapped inside as you explained). Some leave tiny dimples on the surface.

If I prefuse the glass, do you mean these bubbles in the flaw will hopefully come up to the surface in the first fuse, and then somehow even out on the second firing? The second firing has to be full fuse because of the tekta base.

If this is correct, would you have a suggestion for a basic schedule for this first fuse, to give me a starting point? So that I don't get much distortion/dogbonning (since at this point is only one layer), and it flows enough for the bubbles to get to the surface in the flaw area.

Hope I have understood this right. Sorry about asking for a schedule idea, have never fused a large single layer piece .

Many thanks for your help, seachange