* Sn - Will be found at the low ppm levels. Will not effect etching performance*.
* Pb - Data from the Alcatel plant in Austria shows average levels of 22 mg/l. At this level there is no effect on etching.
* Fe - Will not build up due to the insolubility of iron in this system.
* Cr - Present at low ppm levels has not been a problem.
* Zn - Present at levels of 2 to 4 g/l. At this level there is no effect on etching.
* Ni - Has never shown up in the systems that have been analyzed.
* As - Present at low ppm levels.
* SO4 - Data from the Alcatel plant in Austria shows average levels of 4.2 g/l. Levels below 10 g/l will have no effect on etching.

* The concentration of tin and especially lead in etchant is dependent on the chloride concentration of the etchant. To minimize their levels, the chloride concentration of the etchant should at all times be kept below 5.9 Molar.