I cannot figure this out for the life of me, but the odd slab in the odd oven with come out with sugary portions. Other slabs from the same run don’t have a spec end to end, but then others, like these have sections that are sugared over. What are common causes and what can I do differently.
Thanks a lot folks! 
Thca leftovers from previous runs which end up in slabs and cause nucleation?
How clean is your oven?
I thought that too, but it seems to be sporadic, some runs out of the same oven come out perfect, and others come out like this.
I think it might be some form of cold crashing during recovery, putting little Thea crystals into the solution that then come out into the slabs. Could be wrong though.
However, if that’s right, what can I do to change course?
You can take a heat gun to it and get it all back to its glass transition state with minimal decarboxylation. Edit: Do this after the butane has evaporated of course
If you think you’re cold crashing mini THCA diamonds during recovery, maybe pour out the extract when it’s a little wetter? FWIW I do not make shatter so take my advice with a large grain of salt!
Maintaining pressure during recovery can help avoid unwanted precipitation. You can also stop recovery towards the end, and let it warm up and redissolve before recovering the last bit to pour.
If it’s happening after you pour, it may be a moisture or agitation issue.
Sharing your purge SOP would help. What temp are you at?
Pouring with too much solvent should be avoided, as the evaporative cooling will only exacerbate the issue.
Also, probably not great to be pouring straight onto parchment.
Could also be moisture (ambient humidity), media that got though your filter stack, or “seeds” in your oven, collection, or pour spout…
Guess it could also be schmutz (particulate) settling on your boats because sometimes you make them and let them sit for hrs before pouring.
Why shatter?
Cut the portion that nucleating out(using tools).The crystallized area will spread through the whole tray and turn everything to “sugar” if you don’t remove it. I’ve used commercial-kitchen-grade stainless steel scissors and dough-cutters to remove sugaring sections successfully.
Even a good bump on the tray can start the nucleating process. Most likely, it is particulate contamination or THC-A seeds getting into your shatter. Dirty trays, dirty parchment, etc. If you are a high-throughput lab, you may have THC-A “dust” suspended in the air and settling into your trays. Sharing more information on your set up, environment, and SOP is key to solving the root cause.
5 easy steps in the mean time:
Step 1: Clean the shit out of everything.
Step 2: Clean again!
Step 3: Be way more gentle on your pour-off, and handling of trays.
Step 4: SLOWLY pull vacuum. Don’t let it muffin too much, or at all if you can control it.
Step 5: Realize shatter is a stupid product to manufacture and start making sugar and batter to make life easy and profitable.
Technically, under vacuum, water boils off next in line after butane, before the terpenes come out.
All terpenes have a higher bp than water from what I have found… to which I have a pretty long list of cannabis terpenes, the lowest I have found boiling around 105c. Which we all know water boils at 100c.
I have even tried intentionally putting water on a slab many times and it never had any effect just to see if we could force it to sugar out that way. Zero effect.
Really you just need to get to the right solvent ratio / temp and it will start to crystallize in spots. Don’t forget terpenes are solvents!
I have also found that with high propane blends you can get to a really nice shatter by doing a much hotter purge for a much shorter period of time. Or just melt some THCa in there. 
Have you tried letting it sit not under vacuum or introducing it before pouring the slab?
True, making shatter is almost a race. Can’t let it stay in that zone too long.
Yes. I have put it through the ringer trying to get water to make shatter turn to crumble / sugar.
Interesting. I haven’t made any shatter in quite some time, but looking back I honestly can’t say I ever had any first hand issues with moisture causing slabs to sugar. I just know it was always thought to be an issue.
Working outside, once upon a time, i certainly saw what seemed like seasonal differences…
…and production got easier once we were able to move inside.
I’ve definitely noticed seasonal and regional differences as well, but I can’t necessarily attribute any sugaring to be a moisture issue. At least not with any level of certainty.
The material is not properly cured.
THCA=DIAMONDS
THC=OILY/FLAT
And the terps too need to be heavy to help stabilize the particles from nucleation
TERPS=ORGANIC SOLVENT
Poppycock
. Wtf
