"What Is This Growth On My Mugs After I Microwave Them?"

Answer: "Ceramicist here. So clay bodies are porous, depending on the material. Porcelain is dense, and earthware and stoneware is less. Either way liquids can move through fired clay. Glaze that goes on the outside can look solid, but can have hundreds of tiny cracks and holes. When you microwave liquids or just let them sit in a ceramic vessel they can seep through and crystallize in the cracks and holes. This usually only happens with hand made or cheap ceramics."
Pretty sure you are wrong.... the black/blue pages in those are thin. photo looks more like an album.
Better... er... what? That would depend on the specific function of the slide rule. I used these in an engineering drawing office early 70's
#56... That is what is left after removing a metal screen that was painted at one time
came with firearm accesories... Probably a wick for old gun.
But the two things can look more or less identical.