artifact line
Hi,
you where talking about artifact lines in clear glass - and when I understood that right it is not clear how they appear or how they can be avoided.
Here is a little science..
When you hold glass into the flame the flame glows orange - sodium (and who knows what else) in evaporating from the glass.
Sometimes - while working very hot with a pointy flame you will find a little haze around it - which is sodium haze that condensed on the colder glass around the working point.
So the glass changes in the flame. On the surface like just described - but also inside the glass a lot. Mainly due so called sodium migration.
As a rule. The hotter the glass, the stronger the flame and the more/longer you have glass is in the flame - the more the glass changes!
In the here described case it has nothing to do with the opal.
It is only the clear glass and the flame that causes this effect.
Of cause the two different kind of Boro that where used will make a difference.
But the main thing...
- Sealing the opal in the tube first, lots of heat was used.
- Then later a big solid clear was heated a lot in the flame - the glass on the surface changed a lot (mainly sodium lost)...
- ...and then the opal was squeezed into that.
- Doing that a lot surface glass gets pushed away (similar to the head making a mushroom bead) and gathers in a circle around the opal.
So here we are - a circle around the seal with a lot of changed glass. And this glass simpy has a different refraction index then the boro around it. That is what gets visual as these lines.
There is not much to do - since you can melt glass without a flame!
Best is Larry's advise - working backwards.
Otherwise try to keep it in mind the glass changes in the flame and when it matters work cold and in a smooth flame.
But very often it is a contradigtion of what you where planing to do....
Hope this helped a bit - sorry about my poor English. It's not my first language!
|