problem with my marbles

[Onekura]

Hi - I have this terrible surface on my bigger marbles, that spoils the look. Am I over-heating (which I tried to avoid) or is there an other reason for this? And is there a way to fix it? Flame polishing didn't do it . . .

[cheng076]

I looks to me like you had tiny bubbles, tiny bubbles... on or very near the surface when you rounded it out. For me anyway it is impossible to fix. When I try to flame polish them out the trapped air expands just enough and the marvering smoothes them out just enough that they look 'fixed'. Then when the marble cools the air contracts and pulls the skin of glass over the bubble down into the little divits.

[e. mort]

Hi - I have this terrible surface on my bigger marbles, that spoils the look. Am I over-heating (which I tried to avoid) or is there an other reason for this? And is there a way to fix it? Flame polishing didn't do it . . .

The only way I have been able to fix them is to get the back of marble hot, and pluck out each bubble, one at a time, then re-round. Sometimes after you have picked out the bubbles, you can put in a little bit of glass in each of the craters with a stringer.

This is a very frustrating thing, and is usually caused by poor quality rods of glass with air bubbles trapped in them. However, you can cause this problem for yourself if you end up trapping air between your coils as you are putting your backing color on.

I have also cheated and done multiple layers of a large frit, and sometimes that kind of makes them less obvious.

Good Luck!

[gmkcpa]

Exactly what glass are you using (color & company)? Both of the above responses are right on. If the rods you use have little air bubbles in them try getting rid of the air bubbles in the rod before you use it on the marble, by pre-melting and then twisting the rod all around to get the air out, then pulling it back into a rod to use on the marble. The best solution is to use rods of colors that do not have air bubbles in them to begin with, although this limits what colors you can use altogether.

[Onekura]

Thank you for the great input. To my disgrace I must admit this has happened on the clear - not with color. I used a 16mm clear rod, formed the marble on it, flame cut it off and when I melted everything in it must have happened. I didn't even notice it then. And I should mention, that I took the bubbly flame-cut-bit off before melting in. The glass used was Simax clear. And it happened again today . . . and I was so careful not to boil it . . .

[cheng076]

I always try to remember to melt/pinch off the end of clear rods before useing them again as I always seem to boil the tiny tips as they are pulled off leaving a tiny bit of bubble scum. Color, not so much, as I am super careful not to boil the ends.

[Mr. Smiley]

Is there a chance this was the side of the marble that was on the kiln floor? Did you see this before it went into the kiln?

[Mr. Smiley]

My other thought is that you're picking up dirty stuff some where along the way... is your mold clean? You tools rust free?

[Onekura]

No, this was not the kiln side down and I always clean my marble mould - shouldn't be that. My worry is over-heating, because this only happens when I do big marbles - never on small marbles or pendants. The idea of airbubbles makes a lot of sense because I can't see it while working the marble. And I did a lot of fire polishing to get it nice.
Thank you all for your help. It is so frustrating, putting all this work into it and then having those "dents" spoiling the look. Those big marbles use up a lot of very expensive oxy . . . sometimes I wonder if it is worth it . . . . maybe I should stick to pendants . . . .