Something the man did mention, but which I probably underestimated, is that some of the bricks were contaminated with (light) fuel oil. In Belgium, some fuel oil had a red colorant added to it, for which reduced taxes applied. Many of the bricks have some of that red color, but don't strongly smell of fuel oil + seem dry. Some, however, were clearly soaked in fuel oil. Unsure what to do with it, I built a dry stack J-tube in the hope to burn off most of it.
3 burn videos on my YT channel:
https://youtube.com/shorts/z9melpBBixg?si=C1bzKGLxKHrWqtUf
I was pleasantly surprised with the J-tube performance as well, and of course every excuse to make a fire is a sound one...
In the end, I could see the bricks 'drying' up. Some smoke left on the outside, and I assume a lot was burnt by the J-tube from the inside. Will probably have to repeat to get the most of it out, but at least it was already having an effect.
Anyway, thanks to all of you for keeping this forum alive. It's refreshing and energizing to have all this knowledge open source, with everyone eager to share. Quite different from day to day work, I would say. Wishing you all a great (early) Christmas!