Some of that is likely heat coloring as well. I would make sure they are clean, but unless you have the valve inspection police with fiber-optic scopes checking your engine, making the color pretty (until you run it again) will be a lot of work for no gains. I am also shy to suggest any additional work as any contact of abrasives or even an accidental nicking the seating surface with the nut on the mandrel will force re-grinding the valve. I just soak them in cheap injector or carb cleaner over the weekend and scrape off the **** with a soft brush or tool.
ya, i was kind of wondering about the way he cleaned them to start with.. the thing i was talking about is usually a soft medium in a vibrating 'tub' of sorts... used to clean brass casings for reloading bullets... dang sure wont hurt a SS valve, or its seat...
The valves will need to be very lightly touched with the grinder before they go back in my engine. The seats also need to be hit. I don't know yet if I need new guides or not so they would have to be hit anyway if the heads need new guides.
I used the brass wire brush with my cordless drill. The brass is softer than stainless so it leaves no scratches on the valves. The thing got away from me and left an interesting design down my hand though. I am at least knocking all the old carbon off so they are essentially clean. They just are not shiney any more. I have heard of valves being sand blasted or perhaps they were bead blasted but I think those were stock, steel valves so I don't plan to try that.
I may try a little aluminum or chrome polish on one and see how it does.
I've chucked the valve stem up and spun them up in a drill press or lathe before to pretty just the face up for the customer to see in the chamber on head jobs, but my point is that anything abrasive enough to clean the back of coloration is risking the sealing surface, and that's unnecessary risk to me, as clean is functionally perfect and you can't see it once assembled anyway. Cleaning the face can be any clean-cutting abrasive including Scotchbrites and sandpapers. Something like lapping compound on a rag or leather pad would leave it silver but dull.
Hit your valves with a steel wire wheel doing 3600 or so rpm and rub that crap off. You will NOT endanger your seating, It's the route I use on all valves even when not re-grinding. It's never ever even marked a valve doing it this way. They are far too hard.
Of course, this is with the valves i your hand... not installed in the head.