So Dave you're not so hot at writing - don't worry about it I'm red hot at reading 
You're getting there it takes skill - you have to learn that skill - mainly through doing it and patience and sadly doing it wrong. When you do it wrong pick yourself up have a cup of tea
and just do it again, it is all part of the learning process.
So we could say so far so good . The black gunge will come off the metal with some solvent - paraffin (kerosene) , turps lacquer thinners. It does need to be wiped off the metal every so often.
If it is on the wheel try (very carefully ) to wipe it off on some scrap metal (no solvent) no solvent on your wheel.
As you are finding out it is a slow job and there is no way to do it faster. Take your time be patient and careful, using a rougher grade will get rid of the extrusion ridges quicker but you may end up with many deep scratches which you will still have to get rid off.
To move to the next wheel - from me yes try it, nothing to lose (only a bit of time) see how it goes.
By now you should be understanding that it does require some skill.
DaveH
You're getting there it takes skill - you have to learn that skill - mainly through doing it and patience and sadly doing it wrong. When you do it wrong pick yourself up have a cup of tea
and just do it again, it is all part of the learning process.So we could say so far so good
. The black gunge will come off the metal with some solvent - paraffin (kerosene) , turps lacquer thinners. It does need to be wiped off the metal every so often.If it is on the wheel try (very carefully ) to wipe it off on some scrap metal (no solvent) no solvent on your wheel.
As you are finding out it is a slow job and there is no way to do it faster. Take your time be patient and careful, using a rougher grade will get rid of the extrusion ridges quicker but you may end up with many deep scratches which you will still have to get rid off.
To move to the next wheel - from me yes try it, nothing to lose (only a bit of time) see how it goes.
By now you should be understanding that it does require some skill.
DaveH