Etching SPP with ferric chloride

[Iulistoi]

I bought 1 liter ferric chloride to etch my SPP packing. It is 40% concentration and I have 3 kg SPP or about 2.6 liters. The questions are:

1. Should I use the undiluted solution?
2. How long should I hold the SPP soaked in ferric chloride?
3. Is it enough to cover all the springs or I should buy more?
4. Rinsing with just tap water several times is enough for cleaning all the corroding solution?

I know somebody whose SPP gained a strange color after etching, suspecting it was rusting, but it cannot rust, being stainless still. So the conclusion was he did not wash well the SPP.