Black veining Or web effect

[Vince]

I'll try answer a couple of posts here. First, Moretti/Effetre Opalino glass is not quite compatible with the other glass of the series, and some, the Carnelian for example, is particularly incompatible. Therefore, mixing this glass with others is likely to produce a bead that is not durable. One series that I made that used ONLY opalino glass, but mixed a green base with small amounts of rose and white, cracked, even after being well annealed. The first cracks took about a month or more to begin showing, and many of the other beads began indicating cracks over the next six months to a year. After the first 18 months, the rate of cracking declined to zero and I have had no beads in the batch crack since. But, I lost more than half the beads from the batch to stress cracking. Will the others crack over time? I don't know, but it is very possible. By the way, these beads were made over a period of about a week, so it was not an error in any one session that contributed to the problem. There were about 50-60 beads in this particular sample.

On the other hand, I have used the Nile green as a core for beads that were multiply cased in various transparents, and those never showed any cracking. In this case it was the proportion of glass that kept it from happening because the Nile green formed only a small core completely surrounded by large amounts of glass that overcame the small amount of stress in the core. It is the same characteristic that allows one to make a paperweight with Moretti constructs in the interior and then Schott S8 as the encasing glass. There is indeed stress, but it cannot overcome the strength of the surrounding glass and cause a crack.

As for whether or not one can predict that a bead will or will not crack, I don't think there is any way to do this. If the bead is transparent, you can use a polariscope to examine it for stress. If it is opaque, you probably cannot tell. The real problem is that cracking does not follow a schedule, and may happen at any time. The best way to create durable beads is to understand the characteristics of the glass one is using, to use sound lampwork techniques, and to properly anneal the resulting bead. There is no magic, just sound craftsmanship.

The beads that I currently make from opalino no longer crack, but I am careful to avoid those things that I know increase the probability of them cracking. The rules are still the same, practice, practice, practice, and learn from your mistakes. I make lots of mistakes.

Vince

[margi]

Vince--Thanks for all that helpful info, as always...

Ah, ain't it sad. In my early days of lampworking, I played around a lot with opalinos and alabastros, knowing that they were kind of "iffy," but not yet knowing HOW iffy. Some of the colors are so lovely--like the striking copper-- even if the textures are a bit bizarre, and they tend to burn and bubble easily. I didn't do much mixing of opalino or alabastro with any of the other Moretti glass colors, but I did combine colors within their own "type." Fortunately, I didn't sell any of those beads--because practically all of them have cracked, and it took some of them a year before they did!!

Now the remaining rods mostly just sit around gathering dust, unless I happen to think of picking up a single rod to make, say, some copper-colored spacers. I know that there ARE things that I could (relatively) safely try doing with these kinds of glass, but I'm so wary of them that I mostly leave them alone.

BTW, what is it in the composition of these glasses that makes them so incompatible, compared to the other kinds of Moretti glass? Do they all have slightly different COE's?

Margi

[dlbk]

Thanks for your insights, Vince - I'd love to try the Opalino, but it seems so mysterious to me. You mention.."I am careful to avoid those things that I know increase the probability of them cracking". Is there a book you would recommend where I could read up on the characteristics of this type of glass so I can better understand it? I typically dive into things and love to experiment, but it sounds like this glass definitely has strict parameters that I should study up on first.

Thanks,
Deb

[Vince]

Deb,

there is no book. You just need to work with the glass.

Margi, all the glass colors may have slightly different COEs, it is just that the Opalinos seem to be far enough out of the range to be troublesome. The stated COE of 104 is nominal, but not exact.

Vince

[Karen]

I have used both the opalinos and alabastros as 'toppings' on a base Moretti bead but this may be a case where the 15% rule gets taken down to 10%. One of the necklaces I made with these beads has been worn a LOT and after two years shows no cracking.

[dlbk]

>>there is no book. You just need to work with the glass.<<

Dang Vince - I was afraid you'd tell me that! I'll get some of the Opalino and play with it. Just curious - have you gotten to a place with your knowledge where you'd feel confident in selling an Opalino bead - or are they mostly too unpredictable? A bead cracking after a year is wild - if a bead has internal stress, why wouldn't it crack right away, or at least within a few days/weeks after being created? Is it possible a longer time in the kiln might prevent the cracking? I don't understand all the physics involved, but find it fascinating.

Deb

[Elise]

Vince,
Are you sure this is an oxydizing effect? i ask because I got a few beads like this working with opalino on a hot head. I assumed that I had either burned the glass or that it was gunk from the mapp gas...or that it was reduction. In any event, I stopped using opalino on a hot head because i thought it couldn't be worked corretcly. (although in some of the beads it was an interesting and not altogether undesirable effect...just one I hadn't been expecting).

Anyway... I'm tempted to try it out on my minor with reducing an oxydizing flames to see which (if either) reproduces what I got inadvertantly on the hot head. It happened more frequently with white and pink. i could only get clean beads in those colors towards the end of he tank when pressure was relatively low (and the flame cooler).
Aloha,
Elise

[Vince]

Deb,

I sell many Opalino beads, and they do not crack. Normally I keep samples around from various sessions for a long time, and if the samples do not crack, it is likely that the beads are not cracking either. In general, I can make Opalino beads that do not crack as often as I want.

Elise, the "Black Web" effect is not an oxidizing effect and I did not say it was. The "Black Lace" effect using the Moretti intense black stringer is an oxidizing effect and is very different.

The black web effect using Opalino glass is produced by using both reduction effects and oxidizing effects. You need both to do it correctly.

Vince