"William Sommerwerck" wrote in message
...
Acids are what's used to etch porcelain bathtubs for "refinishing"
with epoxy paints. Even leaving chlorine bleach solution puddled
on the tub surface will etch it -- I found that out the hard way.

Which acid or acids? Decades before I saw "Breaking Bad", I knew that
hydrofluoric acid attacked glass and porcelain. But hydrochloric?


I recently discovered that caustic soda in an ultrasonic cleaner is capable
of etching the glaze off of spark plug insulators.