Hull Cell Test Plate Analysis

Hull cell analysis of a plating bath electrolyte is more of an art than a science. While some guidelines do exist, only time and experience (and VERY GOOD record keeping) will provide the tools you need to quickly, and accurately determine the state of your bath.

The key to using the cell is learning to interpret the patterns on the test plate and how they relate to the condition of the electrolyte. Before using a Hull Cell to test a plating bath, analyze as many components as possible using a titration based analysis kit to insure that other components of the bath are not confusing the Hull Cell results

click on image to enlarge	Hook up the Hull Cell to you plating supply with the corrugated anode attached to the positive (+) terminal (anode) and the test plate attached to the (-) terminal (cathode) A typical test with involve plating the test plate for 10 minutes with a current of 2 amps (DC).
click on image to enlarge	Balanced electrolyte with no brightener When you first mix up a new bath with no brightener (or have just carbon treated an existing one), the test plate should look something like this. The high-current burn area will be narrow in extent and very rough and grainy. The deposit at the high-current edge may crumble off in your fingers.
click on image to enlarge	Balanced electrolyte with no brightener and organic contamination If the plating tank was not adequately leached prior to adding the electrolyte, or a carbon treatment has not been effective at removing a contaminating organic component, the test plate may show a narrow shiny region in the low current area. Full carbon treating is indicated.
click on image to enlarge	Balanced electrolyte with proper brightener levels. When everything is in good balance the test plate will exhibit a mirror bright region between 40 ASF and 15 ASF (approx). Depending on the concentration of sulfuric acid (H₂SO₄), the bright region may extend all the way to the low-current edge of the plate. (see below)
click on image to enlarge	Balanced electrolyte with proper brightener levels and high acid concentration The high-current burn region is narrower and the shiny region extends all the way to the low-current edge. High acid is generally not a problem as long as copper sulfate is not being forced out of solution in the form of microscopic suspended particles.