Depending on the amount of clogging of the acid, the first holes may appear after 15 mn -or way more, just check every 5 mn to be sure.
*be careful* of not dropping any acid on your floor or clothes or those are ruined!

After 5 mn of this treatment, you notice that the parts of the plate which were developped begin to turn black

So the point of those pics is to show basically what i do and to present -vaguely for the moment- the devices I have been building.
The red thing is the etch tank done out of a morning chocolate box, which is pierced and plugged to an aquarium air pump.
I take the fret between 2 wooden bits and secure the whole in a strong clamp (If i were to dip the clamp in the ferous oxyde, the metal parts would be attacked by the acid)

Still working with the photoetch plates; here are 4 that will be part of the hull, including the small one which is designed for the portholes.

Now the mastic part, soon it will be sanded and I will add the lower part of the rusted metal plates

Now here are the parts as glued on the lower part of the hull!
Notice the porthole that i rougly cut in the plastic, then I inserted a plastic tube so that the shape would be perfect.

So here are the different parts after cleaning and trimming -the rest is some rivet plates that will be fixed here and there.

I *think* that during all those weeks of trying, I managed to streamline the photetching making process. more on this soon.
Anyway, here's a ravaged looking photoetch set that I left too much in the acid. Why? hey, i needed it to be really very rusty looking, And I think i managed!