But we took a piece of black worbla and a piece of "normal" worbla and compared them during several tests. Sadly I do not have photos of all the tests, my words will have to suffice. Also, due to me running out of time I did not get to test priming or painting. So I will cover that later :)
While cold the black worbla seems "crisper", so we took our two samples and tore them down the middle. The difference was very little, but I have to agree that the black one tore more easily.
But will it break as easily if we heat it up. Out pieces were heated up and gently stretched to breaking point. Here I felt a larger difference. Since the fill material in the black version is smaller and more evenly distributed it also stretched more even when heated. It also stretched a bit longer before breaking.
With this in mind I made a classic "boob cup" and here I could really see the difference. It stretches way more even across the acrylic dome and leaves a more even and less rough surface than normal worbla.
I have on several occasions stepped on my worbla props as they were laying on the floor, I even stepped in the middle of the boob cup on a finished chest armor and it did not take damage (NB: unpainted). But with the black worbla being a bit crisper, would it then crack if you step on it?
This test we actually filmed and I was a little surprised over how well it went.
With a little more heat and shaping over the acrylic sphere it would be completely fine again. But I might recommend double layer of worbla for the boob cups (no matter which version of worbla you are using)
Over heat test
We have all experienced over heating the worbla and then getting bubbles and a rough surface. Again we took our two test pieces and heated them up way longer than necessary to see what happened. It took longer before that black worbla got misshapen and the damage was not as severe as with the normal kind.
With one of the boob cups one person in the audience tried to see if light shone through, which it did not (even though it was stretched thin.) This could be an advantage if you are making small glowing markings and just cut the markings as holes in the worbla and add a large light behind it all.
Rip off or reapply test
It was advertised that it would be easier to take off pieces that were already glued to the worbla. And yes, it was easier to peel off details, but that also means you have to be careful to attach them well so they don't accidentally fall off. Always heat both surfaces.
Ibelinn cosplay had brought with her a prop made using the sandwich method (worbla - foam - worbla) and showed that the worbla stuck very well together at the seams, even better than normal worbla when applied correctly.
We tried to shape the worbla over a foam piece to see how it shows detail and how well it stuck. Very well in my opinion, it stuck better to the foam than the glue holding the foam pieces together.
But can you mix normal and black worbla? Yes, you can. We both tried to glue two trips on top of each other and to knead left overs to one part. Both were a success, but as we did not try priming and painting I cannot say if the surface will be very different (because black worbla is a bit smoother). It doesn’t look that this you be a problem though.
The draw test
With normal worbla you can use a normal marker to draw your pattern directly to the surface. With the black version being so dark you need to use a light pigmented marker (like white or silver) or cover you part in making tape and draw on that to make your pattern.
Conclusion In the end this material is not very different for the normal worbla. There are a few upgraded features as mentioned here, the best one imo is that it is already black and leaves a smoother surface when stretched. Guess I will use a mix.