cause of crack?

orion · #1 2010-02-11, 1:25am

I'm a relative newbie to boro, and I don't necessarily understand the nuances of it after just a few months of once a week 'playing' with boro. I spent about 2 hours working on this turtle, on a minor. When it came out of the kiln, it appears to have a small crack in the clear area, near one of the legs. The legs/flippers are peacock chameleon, which I understand is a chrome color that when reduced can cause some incompatibility. I guess it is possible also that I did not bathe the piece in the flame enough while I was working on the legs, or I did not have smooth enough transitions to the legs. I am unsure of the importance of this, but I have heard or read that it is important. I'm attaching a picture of the turtle, I was hoping to get your input on what you think could have caused the crack(see reflection near upper back leg), and whether I should try to mend it. If I were to do that, what do I do in terms of ramping it up in the kiln? Will the crack likely spread and cause the whole piece to crack off? I have had this happen on soft glass stuff but I don't have the experience w/ boro to know. I mean to keep this for myself as my 'first' boro turtle so if it's unlikely to self destruct any further I'm happy keeping it as is and working on more of them.

Thanks for any help!

Wonker · #2 2010-02-11, 3:51am

With boro, you can't get away with connecting two sections of glass in quite the same way you can get away with using soft glass. With boro where the legs are connected to the body you need to really melt the leg attachements on to the body really well. I can't see very well from your photo. They look pretty well melted in from what I can see, but that might be the problem. Chrome colors sometimes don't like being encased (but it doesn't look like that's the case here). Garaging Chrome for a long time sometimes creates a problem. If I had to guess, I'd say that as you were going around attaching legs, the body cooled too much at that leg and you hit it with the flame. I've done that before, especially when I was first doing these. You have to keep the body warm as you are working it, once it starts on the cooling cycle, abruptly changing that can cause a crack. Looks like a nice turtle. You might be able to put him in the kiln, ramp him up to temp and repair it. This probably didn't help much. Hang in there.

Bunyip · #3 2010-02-11, 8:49am

I was going to suggest repair as well. It looks like it's only in the clear, so you should be good! The crack doesn't look like it was due to color incompatibility, more like the clear got too cold and you hit it with the flame again - but it might be helpful to take a macro shot and crop to just the area of the crack so some of our local wizards can further diagnose.

gmkcpa · #4 2010-02-11, 9:10am

The second 'implosion' turtle that I ever made looked alot like yours. And it cracked in just about the same place that yours did. And I'm positive that it cracked because I did not keep the body warm enough while I was attaching a limb. So now I keep it on the back of my workbench as a reminder. Personally I would not try to fix it because where the crack is I'd probably screw it up more. But if you do want to try, just make sure that you have a spare flipper to attach.

orion · #5 2010-02-11, 9:39am

is it likely that the crack will not propagate? The crack doesn't bother me that much as it is - that is to keep as a reminder, and my 'first' turtle without risking making it worse.

orion · #6 2010-02-11, 9:53am

forgot to say - thanks everyone for the responses so far, it is really helpful!

deb tarry · #7 2010-02-11, 11:56am

I pop things in the kiln all the time to repair or re-work. My son was starting out making small mushrooms that kept cracking due to letting things cool to much on one side then hitting it with the flame by accident. He had some fabulous colour combo's that could not be wasted so I would put them in the cold kiln and let them come up to temperature then grab them with pliers and get it quickly into flame and re-work into a pendant. It took me awhile to get the courage to do this but after a couple of times when I realized nothing was going to shatter I have no fear in doing it now. If you want to re-work do it. Another thing you could do is nip off a piece of a clear rod about one inch long pre-heat that in the kiln for practice.

orion · #8 2010-02-11, 12:35pm

When working a piece like this, do I need to bathe the piece in the flame to a soft glow occasionally, say between working on each limb, or if a particular limb takes too long? I do this with soft glass constantly, however I'm not sure how much to do it with the boro! It doesn't take too much to keep the soft glass warm in terms of heat, but maybe I need to more thoroughly heat rather than flash the piece to keep it warm?

With the soft glass there is a fine line between messing up what you've worked and keeping it warm. I can see it isn't quite the problem with the boro but I'm wondering if I need to give it more time when I 'reheat' for it to penetrate the piece.

thanks so much for your responses so far. this is quite a fun learning curve.

Wonker · #9 2010-02-11, 1:53pm

You know how you get that internal clock always ticking when you are working soft glass? You'll have one for boro as well. You do have to keep it warm if you are going to come back to something like that turtle. Because you have to go around it like that, it's difficult to find one direction that you can work without it getting too cool at the other end...on a small piece like that it's almost better to work tail, head, back leg, front leg kind of thing. As you go you'll learn when you need to heat the piece, you get so fast at them that you won't need to after you've done a few. Looks good...By the way, I'd try to repair that piece, that crack will probably get bigger over time and it's a nice enough piece (not to mention your first turtle) to want to save it.

orion · #10 2010-02-11, 11:27pm

so do I need to ramp it up in the kiln to try to save it?? if so, does it have to be slowly?? I have no idea!

Wonker · #11 2010-02-12, 2:23am

Yep, you need to ramp it up to 1050 or 1100 or so. I think that I would ramp it up just like I do for anything that I'm going to anneal. You'll be able to pull it out, make sure to brush off the area you're going to repair before you put it in the flame....kiln dust (and believe me it's there) needs to be wiped away first. Then melt that little crack back.....stick it back in the kiln...voila.... great practice and you'll have a perfect little turtle.

Bunyip · #12 2010-02-12, 6:38am

With boro you can usually just throw it in the kiln, then turn the kiln on and that is sufficient. A cracked piece may not be as forgiving, so if you're worried, use a soft glass batch anneal program to get the kiln (and your piece) up to temp more slowly, then switch to a boro program to anneal.

orion · #13 2010-02-12, 11:31am

you all are really great. thanks so much, you've been tremendously helpful.