Between 2 and 35 mg/l chloride is added in the form of hydrochloric acid to electro refining solutions to precipitate silver and avoid and avoid "sandy" deposits. From 30 to 100 mg/l of chloride is recommended for bright copper plating with many modern brighteners.
Nitrates were reduced to ammonia at the cathode in copper sulfate baths. A reduction product of the sulfate ion, which is said to have a grain coarsening effect, can be removed by heating the bath and adding an oxidizing agent, but oxidizing agents such as hydrogen peroxide or potassium permanganate are said to reduce throwing power.
In the fluoborate bath, lead is the only metallic impurity known to interfere with the deposition of ductile plates; it can be precipitated by adding sulfuric acid. Besides lead, metals like silver, gold, arsenic, and antimony might be codeposited with copper, but the effect of such impurities are not known.
Organic impurities originating from decomposition of addition agents or leaching of elastomeric tank linings sometimes embrittle deposits, but can be removed by treating the solution with an appropriate activated carbon, followed by filtration, alfa-Naphtylamine was identified as an injurious contaminant leached from certain rubber tank linings. As little as 10 mg/l alfa-naphtylamine caused as irregular tank linings. As little as 10 mg/l alpha-napthylamine caused an irregular pattern of uneven copper plate having ridges and valleys. Treatment with activated carbon is desirable when a new bath is being prepared, especially the flouborate bath, which may be contaminated with impurities leached from rubber shipping drums. An instance has been reported of embritlement traceable to impurities from wood tanks.