Homebrew_PCBs

Clarification....

>sorry, I didn't express myself clearly. the residue is there after
>developing but before going into ferric chloride.

The conventional process uses sodium hydroxide or something similar
here. You apparently have to resort to steel wool...Not good.

>to finally remove the emulsion, i do use screen cleaner. but it seems
>to attack copper. i was told to use bleach or sodium hydroxide which
>can remove the emulsion and won't attack copper... but I'm not so sure
>about that. I use paint thinner and a little more work, and it goes
>away, and thinner surely doesn't attack copper.

The conventional process normally uses acetone here. You apparently use
what you can get. I suspect recommendations to use bleach or sodium
hydroxide were aimed at the previous step above where "unfriendly to
copper" doesn't matter since ferric chloride would be the next step.