How do I add custom materials for the material toolgun?

What file do I have to create for certain materials to be usable for the toolgun?
I know you had to use a .lua file in previous versions of Garry’s mod, but I forgot how that was exactly set up and I don’t know if that’s the case now.
Hoping this is the right place to post.

It’s simply just:
[lua]list.Add( “OverrideMaterials”, material )[/lua]

Thanks, been looking for that for a while.

[editline]forgot[/editline]

In case anyone finds this thread, the path to where that line goes is in “garrysmod\gamemodes\sandbox\entities\weapons\gmod_tool\stools\material.lua”.