""bluing sand"? - I think possibly that is a 'typo'.

Maybe Mark's post should read: "bluing and ....""

I guess that explains why I never heard of it before. Too bad it was not a real thing as it would have been a good explanation.
I have made so many typos, that when I go back and look at my old posts I am sometimes not sure what was intended. I usually look over what was typed before hitting the Post Message button but I see what I intended to say instead of what is actually there.

BR, on your 3 photos #1 definitely look like cast iron packing boxes in the lower right.
#2 on the bolts maybe that is a tempering operation? Ovens are completely different. Looks like the bolts are just stacked in similar boxes. Look at the boxes of bolts on the floor. First ones in are upright and later ones leaning over?
#3 Must be winter time. In the summer I would have wanted that work station a long way from that hot stuff going on behind him.