Casting a hammer head - GIF

Casting a hammer head.

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Previously:

1940s iron casting - video
Casting a bell - GIF
Casting a giant propellor GIF
Casting aluminum ladles - GIF
Casting an aircraft engine in the 1930s - photo
Casting brake shoes - GIF
Lead sheet casting
Sand casting a kettle - GIF

anyone know what the casting "sand" is? it is not any of the ones I'm used to seeing, and as the head is demolded, the sand appears almost stringy against the hot metal.