Etching is a controlled sideways problem as much as a downward one. The etchant attacks in every direction at once, so as it eats down it also eats under the resist, and the resulting undercut is what decides whether fine detail survives or collapses.

Additive oil controls that. It forms a film on the freshly exposed side walls that slows lateral attack while the floor of the etch keeps cutting, which is what produces a shoulder rather than a mushroom. The range covers both zinc and magnesium formulations because the two metals do not behave the same way in the bath.

Positive plate developer completes the chemistry. Matching plate, developer and additive from one producer removes the most common cause of inconsistent results, which is a process assembled from three suppliers who each assume something different about the other two.