The chrome deposition turns dark

It is normal for chrome to appear dark in the initial stages of deposition. This is because the chromium layer is initially very finely crystallised, which means that the light is reflected differently and the surface appears dark. As the deposition progresses, the crystals increase in size and the layer gradually becomes lighter and takes on the typical chrome colour.

It could also be that the current density is too high. If the current density is too high, the chromium layer will deposit too quickly and unevenly, which can also lead to a dark or black surface. A lower current density ensures more even crystal formation and therefore a lighter and more even chrome layer. A compromise between speed and quality must be found here.

Another important point is that the electrolyte becomes too warm due to the high current density. Too high a temperature also leads to dark colouring of the layer. In this case, the current density would have to be reduced or the deposition interrupted.