There are several options depending on how shiny you want the surfaces, what shape you want the bowls, what equipment you have and how much work you are willing to put into it.
It all comes down to either 1) avoid the texture in the first place or 2) removing the texture after slumping.
Here are some ways to avoid ever touching the mold:
Drop rings (optionally cutting off “brim” when done)
Slump into a mold – but not long enough to let it touch the sides
Slump at such a low temp (long, slow slump) that the glass doesn’t pick up the texture
I can think of two ways to remove the texture:
Cold-work the piece
Use a product like “Back Magic” that let’s you fire polish below slumping
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