Why do Implosions crack?

Angel · #1 2006-09-12, 10:30am

Hi everyone,

I need some help.... started with boro last week, and some of them turned out - well, not that bad... (The have shape and color, and I read in a thread before, that this would mean a certain success

)
BUT: three of three implosions cracked, the first while cooling, the second one hour later and the third - after heating till the mandrel is whiteglowing! - one day later....

There are always some tiny or even bigger airbubbles with sharp edges around the mandrel, I think, thats the reason for the cracks.
Is it generally possible to work boro implosions the same way as with soft glass? (after all, it is also a heavy test for mandrels and the bead release...)

I work with the german ISIHEAT and an Oxygen Tank, so the Flame should be strong enough, but that stuff is even stiffer as Lauscha-Clear on a Hot Head...

Greetings from Switzerland
Angela

Angel · #2 2006-09-12, 10:37am

PS: Before you ask... I have no real idea, what kind of color glass I used... Think it was a kind of Northstar silvery dark blue, which turns green in oxy. I had it from a Friend, only a small piece, for testing.

e. mort · #3 2006-09-12, 10:51am

post some pics so we can see what you are getting. That will help to figure out what is going on. Also, what temperature is your kiln?

Cosmo · #4 2006-09-12, 11:05am

What kind of clear are you using? Also, you mentioned a mandrel... what kind of piece are you making?

suzanne · #5 2006-09-12, 10:41pm

I'd love to see some pictures as eric said. Some greens are known to crack when encased, but I have never had any piece crack on me while working it. Boro is very forgiving when it comes to thermal shock, so my guess is something else is going wrong. Could it be you grabbed a wrong rod of clear ( maybe lauscha instead of boro). This could explain the cracking while working it. Also , you might be letting the piece go way too cold before flamestriking it, that could be the problem as well.

Suzanne

Angel · #6 2006-09-13, 12:12am

Hello,

so I try to show som pictures (hope, it works, its my first time

)

These are the cracked ones, from left to right as I worked them. The cracks became smaller, at least that.

This is the color, nearly black with silverish shine, and bluegreen when pulled tostringer.

And this one is intact (until now...); I made a very thin barrel first, then the disk on one end and the color with stringerlines, not dot. With the barrel I tried to prevent from breaking loose from the mandrel.

All the beads are between 1.5 an 1.8cm (no idea whats in inch, sorry) quite small for my usual size. With softglass, I make barrels unto 7, 8 cm...
For mandrel, I used 2mm size, but thats quite dangerous (for the mandrels) so I think to choose 3mm next time. Bead release is at the moment super blue sludge, which works not bad. Foster Fire heavy duty breaks after short working time, when the mandrel cools after strong heat. (Small pieces pop off like gunshots, have you ever seen that!!!!

)

So, thats all I can say for the moment... Thanks a lot!
Angela

Angel · #7 2006-09-13, 12:18am

oops, forgot.. I didn't put them in the kiln (only in vermiculite), because I thaught, that's not neccessary for boro??? Only with these striking reds I do batchanneal, on 1150 ° F, which is 620 ° Celsius. Would that be the annealing temperature for putting them directly in the kiln? And does boro need a cooling ramp?

Angel · #8 2006-09-13, 12:30am

PS2: I cleaned up my working place before starting with boro, and I have the Boros completely separated from the soft glass, so I'm sure, it was not Lauschaclear. And it was so stiff, impossible

Lauscha at that flame flows off... The clear rods are Northstar, 4 to 5mm. And I have some colored boromax, from a test set. maybe I try these once, there is a color which seems similar to me; 987 Amazon Night.
Now I hope, that was all

Greetings and thanks!
Angela

suzanne · #9 2006-09-13, 3:13am

Those look like incompatibillity cracks to me, some greens definetly cause trouble when encased. Do use 3 mm mandrels next time cause you will burn through the 2 mm ones very fast.

suzanne · #10 2006-09-13, 3:18am

Quote:

Originally Posted by Angel

oops, forgot.. I didn't put them in the kiln (only in vermiculite), because I thaught, that's not neccessary for boro??? Only with these striking reds I do batchanneal, on 1150 ° F, which is 620 ° Celsius. Would that be the annealing temperature for putting them directly in the kiln? And does boro need a cooling ramp?

Boro does need to be annealed. I am not sure who told you that it wasn't neccesary but they are wrong. Boro is more forgiving then soft glass when it comes to thermal cracks but you do have to anneal them to release the stress in the glass.

When I batch anneal I always put my beads in vermiculite, and I haven't had a single thermal crack in my boro beads ever but I guess that is just plane luck. I batch anneal boro by ramping up full speed to 615 and hold for 30 minutes ( temperature is in celcius). This is a striking temperature and causes the color crystals in the glass to grow. Then I ramp down with 1 degree celcius per minute to 515 and hold for another half hour . Then I ramp down with 1 degree per minute to 440 and hold for 15-20 minutes for small beads, 30 minutes to 45 for big beads. THen I turn my kiln off and let it cool by itself.

When I anneal boro imediatly I garage them at 480 celcius to prevent any striking, when I am done making beads I ramp up full speed to 615 and I repeat the procedure as mentioned above.

Suzanne

e. mort · #11 2006-09-13, 7:14am

Every boro bead that I have made and cooled in a fiber blanket has done this. I think it is thermal shock. When I started putting them right into the kiln the problem went away. (I use Sludge Plus for my release.)

I think the color you are working with is NS Blue Exotic. I have never had a cracking issue with it, and I have really deep encased it in some marbles.

suzanne · #12 2006-09-13, 8:16am

you are kidding eric, did they all crack??? Howcome mine don't crack when putting them in vermiculite, curious minds want to know

hotflashwanda · #13 2006-09-13, 9:08am

Northstar recommends that all the Exotic colors (including Red, Blue, Green, and Aurora) be carefully annealed when encased to prevent cracking and checking. I once asked someone with the company what that meant, and their reply was putting the pieces directly into the kiln as they are made, not overannealing at high temps, and having a conservative rampdown schedule.
I've always done this, and never had any cracking with exotics.
Anita
www.fireflybeads.com

e. mort · #14 2006-09-13, 10:03am

Quote:

Originally Posted by suzanne

you are kidding eric, did they all crack??? Howcome mine don't crack when putting them in vermiculite, curious minds want to know

Yep, every dang one of them. The wierd thing is that if I make something of the same size or even bigger OFF mandrell, no cracks.

suzanne · #15 2006-09-13, 10:45am

That is weird eric, I wonder what causes it. Maybe one of the hardcore boroworkers is willing to chime in on this cause I am really curious why it did happen to your beads, and not mine, and why you can put off mandrell pieces away without cracking.

Btw the first bead ( the left one) could be a thermal crack but the other cracks are a bit too random to be thermal but I could be wrong off course. The thermal cracks I have seen are always straight down the mandrell, very crisp cracks

Suzanne

Angel · #16 2006-09-13, 1:06pm

by the way... none of my other beads of this combination cracked...

Look at these:

only cooled in Vermiculite (I stick them red hot glowing in, and they keep the heat for hours, my vermiculite is in an old "Friteuse", the thing for making french fries...)

Maybe the tiny bubbles with sharp edges were the main problem, thats why I asked, if boro-implosions should be done different than softglass ones. Till now, I can't bring the glass to flow completely to the mandrel.

Thank you all for your answers, I think, I'll give it a try with thicker mandrels, more heat to make the glass better flow and maybe annealing immediately in the kiln.

have a nice day!
Angela

AVCKimberly · #17 2006-09-13, 7:56pm

I cool all of mine in a fiber blanket and then batch anneal as well. I very, very rarely have one crack. It's normally because I have done something stupid like encasing sparkly green colors. (Yeah, I know....newby mistake!

)

I do have to say that I stole one of Lori's tricks. I have two cake pans that I made a claim shell from. The top and the bottom (inside the pans) are stuffed with fiber blanket. I am sure that it holds the heat better than fiber blankets alone. It takes a good hour for my average bead to cool to the touch. I am also constantly adding beads which keeps it warm until I am done working.

Sorry I am not much help Angela. I haven't uses vermiculite in years. I couldn't stand all the dust.

hotflashwanda · #18 2006-09-13, 8:06pm

Angela, the beads with the bubble eyes have a clear base, with a thin layer of the Exotic color, and clear on top. That is one of the recommended ways of working with the exotic colors to prevent checking/cracking, to sandwich the color in between layers of clear. I notice in your implosion beads the color is next to or close to the mandrel and also the color is thicker than the thin layer in the bubble eyes. Perhaps that could be the reason one set of beads survived and the other didn't.
Anita
www.fireflybeads.com

Angel · #19 2006-09-13, 11:25pm

Aaahh, thanks Anita! That maybe also would be the reason, why the one with lines and a clear center survived! So I try that next time, I really love the look of the implosions, thats why I started at least with boro... But it has to wait til next week, have to do some soft glass orders first.
Kim, don't say sorry... The idea with the cake pans ist great! I hate touching the fiber blankets, thats why I don't use them

But this could work also for me.
Vermiculite dust is only a problem with cats in the same house.... my friend Anka have to cover all the Vermiculite when she leaves the working space, because her cat - ehem.... I have no cats, and my children are old enough not grabbing anymore in everything with the look of sand *lol*

Angela

suzanne · #20 2006-09-14, 1:02am

roflol... vermiculite makes excellent kittylitterstuff

. My kitten digs in it whenever she gets the chance ( read...when I am not paying attention)

Angel · #21 2006-09-14, 2:47am

yammy, if you ever forget to cover....