I learned the word "seacoal" when I was working in a foundry as a summer job. I don't know
exactly what the molders used it for. I have read elsewhere that the term refers to low grade
coal found near surface in places partly under sea water, or under sea water i;n the past.
From the Internet:
"For years, the effects of seacoal and seacoal supplements have been
evaluated in green sand molding. Changing government regulations,
however, have required an even greater need to understand their
emission characteristics. Therefore, a series of investigations
concerning the emissions of benzene were recently completed and
presented at the 1997 and 1998 AFS Casting Congresses.

Within these investigations, all of the primary seacoal and seacoal
supplements were evaluated. These include: seacoal (bituminous coal),
anthracite, gilsonite, causticized lignite and ground coke. The selection
of these materials was based upon a few basic principles that included:
availability of the material to the entire foundry industry, sufficient raw
materials reserves, suppliers' potential blending capability and costs to
the foundry industry."