Bill, now you need to find some small iridescent organ crystals to simulate a slag load that can be dumped.
Ron
Hi Bill, no that is not what Lionel did. Years ago MTH came out with a set of three slag pots. They are empty so I thought of doing this to them. Then though better of it and later picked up the Lionel set of YS&T "lighted" pots.
This is an image of the Lionel Slag Car. As you can see there is a plastic molded insert that appears to be of orange color but much of the surrounding area painted blackish.
Here running the set with the Alco S2 YS&T swisher.
Probably find something in an Art and Craft store such as Michaels and/or Hobby Lobby. Stuff that might be glued on to drawings kids might do or better yet where stuff foe jewelry makeing.
Ron