Anyone here uses Sodium persulfate for etching ?
Generally speaking in Poland it replaced Iron Chloride for many people.
A local company sells Sodium persulfate crystals as a well known B327 etching product.
You purchase a bag full of white crystals, then you dissolve it in water which has to be heated up to around 40-50°C.
At 50°C the process is a bit faster than at 40°C but faster etching means higher risk of small tracks getting etched.
Variable temperature means the etching speed can be controlled as required.
The solution at lower temperatures will still etch, but it will be painfully slow.
I don't recommend higher temperatures, not really worth it as the stuff gets messy (either toner is dissolving or something is breaking down chemically, lots of black stuff appearing in the water).
Never really had problems with thinner tracks getting etched away though.
Instead of following the procedure written on the B327 package which says "disslove X amount in Y amount of water" I just dissolve more each time the etching process slows down or just stops alltogether.
When the process stops the pure copper gets "dirty", most likely from byproducts of the chemical reaction.
Once you add more the copper instantly becomes "clean" and the process starts again.
The etching solution is fairly transparent (gets blue over time but still nothing serious) so one may observe the etching process in detail.