If you have a one or two pieces of cast iron that you want to clean, electrolysis and lye bath may be a little over the top.
You can easily use oven cleaner – the cheap walmart brand works fine – just make sure you buy the yellow cap spray. The blue cap doesn’t contain lye (sodium hydroxide) or not enough to do the job.
The process is easy, put your piece in a garbage bag – do this outdoors – and spray ever inch of it liberally with the oven cleaner. Close up the bag and leave the piece in a warm location for probably 24 hours. I usually give it another spray after 12 hours.
Take the piece out, give it a good scrubbing with stainless steel wool. Repeat the process as necessary. It may take several application to get the piece clean.
Be patient and good luck.