current is desirably used in the range of 200 600 volts preferably the voltage is at least in increasing order of preference 200 250 300 350 400 and at least for the sake of economy not more than in increasing order of preference 700 650 600 550 direct current is preferably used although alternating current may also be utilized under some conditions however the rate of coating formation may be lower using ac the frequency of the current may range from 10 to 10 000 hertz higher frequencies may be used in embodiments where ac power is used 300 to 600 volts is the preferred voltage level in a preferred embodiment the pulsed signal may have an u201c off u201d time between each consecutive voltage pulse preferably lasting between about 10 as long as the voltage pulse and about 1000 as long as the voltage pulse during the u201c off u201d period the voltage need not be dropped to zero i e the voltage may be cycled between a relatively low baseline voltage and a relatively high ceiling voltage the baseline voltage thus may be adjusted to a voltage that is from 0 to 99 9 of the peak applied ceiling voltage low baseline voltages e g less than 30 of the peak ceiling voltage tend to favor the generation of a periodic or intermittent visible light emitting discharge while higher baseline voltages e g more than 60 of the peak ceiling voltage tend to result in continuous plasma anodization relative to the human eye frame refresh rate of 0 1 0 2 seconds the current can be pulsed with either electronic or mechanical switches activated by a frequency generator the average amperage per square foot is at least in increasing.