Cracking issues
 

Imade my first 2" marble today, and it came out nice except that the Indego Adventurine that I used for the back cracked all around the equator of the marble with what look to be incompatability cracks. The cracks are only as deep as the Indego Adventurine, nothing extends into the clear.

I annealed it at 1030 for 1.5 hours than ramped down to 910 at 300 degrees per hour.

Did I over cook the Indego Adventurine and change it's COE? Should I have soaked it longer? Ramped down slower? This is my first big piece, I'm kind of disapointed that it cracked like it did.

ETA:
I misspoke The 300 dF/Hour is incorrect, it should be 55 dF/Hour.

you didn't use 104 aventurine?

No. It didn't melt that nice. :)

I don't think it is possible to put 104 and boro together. The Adventurine colors can be challenging in some applications. If the adventurine end of the marble was the last thing you put on your mib, perhaps the marble was not evenly heated when put into the kiln? Maybe someone else knows about this color? I would try putting it back into the kiln, soak it for 2 hours and then try to add some clear frit to the cracked side of it, to see if you can mend the crack. I think with boro, some of the colors are stiffer than others, with clear being softer than most colors, that they heat and cool and expand and contract at different rates, which makes them seem in compatible in some uses.

I applied it once Ihad the back of the marble rounded out, before I made the lense. I had problems getting the equator to melt in smooth so I really put the heat to it. I noticed when I put it in the kiln that the very core was still a dull red.

ETA: I've inadvertantly mixed 104 with boro when some 104 clear got mixed in to the boro clear at CMoG. It cracked almost before it went into the kiln. I was just starting out so I didn't realize how fast the 104 melted as compared to boro.

Here is a photo of the cracking.

http://i1197.photobucket.com/albums/...ps8e60e0bd.jpg


And the front:

http://i1197.photobucket.com/albums/...ps36daa879.jpg

When you really pour on the heat to something it usually means you turn up the oxy and propane and allot of times it is more propane than you should for the sparkly colours which cane cause cracking. that sucks.

I was wondering if I might have over cooked it. Time to get some bigger infinite rim molds. I was having issues with the equator smoothing out, I think Ispend 10 minutes pouring heat into the equator, I don't think I had a reducing flame but it may have been. First day with the new torch. I do love the torch, I posted a review in the torch room.

Deb, Would I be wrong in assuming if I were to coat the backing with a small amount of clear, like frit or powder, it would provide some insurance against this issue?

Hmm I don't know for sure you would think so but I haven't played around with sparkly colours enough to be sure. All I know for sure that it it is hit with a reducing flame the chances of cracking increase.
If I can give you a tip about rounding out the big ones it would be get lots of heat into it then work on the spots that need smoothing (say 1/2 inch) at a time and really pour on the heat till the spot is smooth (you can see it smooth out) and don't use the mould just pour on the heat in that one spot, and going around the marble in this manner, when you have gone all around the piece pour on more heat all the way around then a little more than you think then….. use your mould. Everytime you use your mould it draws more heat out of the piece so then you have to chase the heat back in. Hope this make sense ask question to clarify. I try to use the mould as little as possible.

I dont know this particular Aventurine but I do use A LOT of TAGs sparklies Like Heavy Blue Leprechan. Reducing them can cause compatibility issues so I always work them in an oxidizing atmosphere. 300 degrees an hour sounds very fast to me. I will check my program tomorrow and let you know what ramp rate I use when going through the strain point. Also for anything thicker than 1 inch I use a 2.5 hour soak at 1050. This is loosely based on the theoretical tables I have for annealing.

Encasing the aventurine can help as long as you do not use ANY reduction in your flame as you are applying the clear. The issue here more than likely is too much fuel in your flame. You can deep encase aventurines and greens etc as long as you avoid reduction. I have learned this through trial and error and then deliberate experimentation. I use a lot of deep encased sparkle colors in my work. I had to solve the issue. The smallest amount of reduction can cause the cracking. Just make sure you crank up the O2 and this should no longer be a problem.

Thanks all, I can see that going bigger creates a whole set of issues that is not apparent on smaller pieces. I definitely like making the bigger mibs, so I'm going to need to hone my technique. Like I said, brand new torch so I'm still getting used to what the flame chemistry looks like. It looks vastly different than on the Bravo.

I misspoke in my OP. the slow cool rate should read 55dF/Hour, I read the wrong box on my firing schedule.

:) Better! Consider increasing your soak time as well. A 2" marble takes a long time to come up completely to an even heat.

Northstar user manual: "NS-75 Indigo Aventurine: A deep blue aventurine color. Work in an oxidizing flame."

If you didn't work in an explicitly oxidizing flame, I'm thinking that's your problem right there, as the guys have already noted above. Sparkles were my nemesis when I was on concentrators. I've since changed my mind about them but yeah, they're reduction sensitive.

Long garage segments at annealing temperature can cause issues as well.

I probably did have a reducing flame at some point, I was also experimenting with the flames available on my Champion. Now i know, no soft fluffy flames with sparkelies. Is the Northstar website back up? Please define long garage segments, I would assume 6-8 hours or more.

Roy, IIRC, the recommendations were the same as for chrome-based colors, do not garage at striking or annealing temperature, instead garage at 975, anneal as usual. My usual procedure is to eliminate as many variables as possible when I experience trouble, and then introduce them later experimentally once I was able to achieve a consistent result.

At a guess, a 1-hour striking segment prior to annealing probably won't cause checking in most sparkle glass provided they weren't reduced. I've not had problems doing this, but as always in the glass world, YMMV for a lot of reasons.

If you have to garage prior to annealing do it at 950 which is where I preheat prep as well.

Thanks Chris and Larry, I'll change my kiln schedule to garage around 950.

I've used NS-Indigo Aventurine many times as a backing for 1-1/2" to 2" marbles, and never had a cracking or 'checking' problem, but then again I anneal ALL my marbles that size for 5 hours at 1050, ramp down to 960 at 60 degrees/hr, let it sit at 960 for 2 hours, and then my kiln shuts off. I do not open the door, not even for a peak, until the temperature drops to about 150 degrees.

Probably everyone here will say that 5 hours is just a waste of time and electricity, but my marbles don't crack. Even when my cat knocks them off of the kitchen counter and they fall onto my stone floor they don't crack. They bounce.

it's only a waste of time if the mib is smaller then 2".
soaking a 1" mib at 1050f for 5 hours is way overkill. although i must say, better to err on the side of caution.

what is the five hours based on ? My reference material says 2.5 should be good up to 2.5" thick glass.

Gerald, I think the main conclusion was that reduction was the problem, however if you were to couple a long garage segment with your 5 hour anneal you would likely see enough COE shift to cause problems. There was a long article on chrome and sparkle colors in one either glassline or the flow that gave much more specific information based on experimental data but I can't find it now.

Larry: I'm pretty sure that boro manufacturers recommend 1 hour at annealing temperature for every 0.25 inches of piece thickness. I am also pretty sure this is overkill to cover against liability on "adult novelty items" and so forth, though that last is not based on any facts and is merely my opinion.

I would either grind off the adventurine and then rework. Or reheat, and strip off the adventurine, add more color, and reshape. It is a nice marble and it would be worth saving.

i've read anywhere from 15 minutes per 1/4" thickness to an hour per 1/4" thickness. i want to say the Northstar glass brochure says 15 min per 1/4"....i stick mostly to NS color so that is what i based my annealing cycle on. i've had zero issues with cracking, save for my own stupidity in trying to encase chrome colors (fucking millenium falcon looks great deep encased, but will crack every time).

Bunyip, I agree about liability being a "factor" in annealing schedules. Fortunately the science behind annealing has been well researched and we have a wealth of knowledge at our fingertips. That being said, I make adult toys and I am overly conservative with my annealing schedule.

All things being equal, you should be able to put a glass piece that has thickness "x" into your kiln and anneal it for time "Y" and bring it down below strain point at "Z" degrees per hour and it will always be perfectly annealed.

However all things are not equal, the kilns I use are amazing and very high quality but I doubt they would pass as scientifically accurate instruments. I take care to ensure that my annealing schedule has a "buffer zone" so to speak and err on the side of caution.

Also, although I do not have cracking issues with sparkle colors etc, I do not use those colors in the adult toys I make. I also check each one in a polariscope and that is something I don't do with my pendants. So safety and liability can effect the manufacturing process as a whole really.

Otter, I anneal the literal fuck out of everything ;)

You may WANT to say that, but you would be incorrect

http://www.waleapparatus.com/client_...USERMANUAL.pdf

Northstar's website is currently very unhelpful. Thankfully Wale is not. Google is your friend!

well you may WANT to correct me (and in this case you are correct) but i've read somewhere it's 15 min per 1/4" thickness.

annealing schedule argument is like which is the best torch argument....there are MANY answers and most of them work for the person using them.

Luckily this was "what the manufacturer said" rather than "annealing schedule argument". I'll go back under my bridge now :)