Ah, the joys and majesty of wetsanding. It's not that fun, can be a bit tedious, is usually quite messy, but it is in this step that the final product really appears.
In a nutshell, wetsanding is just what it sounds like: sanding, but with water involved. I don't know what the chemistry is behind it, but for some reason, when you sand with a wet piece of sandpaper, you can end up with a rediculously smooth surface. Maybe it's because the powder from the sanded paint ends up fusing into the micro fissures from earlier sanding? I don't know. But either way, the belt is now in for just such a treatment.
I realized I only had 320 grit sand paper on hand, so I needed to head down to home depot to pick up some higher grit stuff for the final sanding job. I grabbed this stuff:
It's found in the paint section, and is specifically designed for wetsanding. If you get regular sand paper, it's likely to break apart once it gets wet.
To make sanding easier, I cut little strips out of the bigger sheets. I'm going to be doing a lot of nook and crannie sanding, so smaller pieces are called for.
I can't really think of a whole bunch of "tips" to give out for wetsanding, other than be patient and go slowly. I guess from a technical perspective, I did something on this project that I would recommend if you plan on going for a super smooth mirror finish. Use two different colors of primer. I started with dark grey, then moved to a lighter grey for a couple of coats, and finished with a couple of coats of dark grey. The reason this is good is so that you can detect burn throughs. A "burn through" is when you sand too far, and go too deep. Worst case scenario is if you sand all the way down to the resin, or worse to the putty. You don't want that stuff exposed in your final master. By using different colored primers, you can see when you burn through, and you'll know when you absolutely have to stop sanding. This technique is really only applicable in the mastering situation. If I was wet sanding a product for display, or a finished piece, I wouldn't want burn throughs showing AT ALL.
So the trick is, go slowly, be meticulous, and gradually increase the grain. Previously, I had sanded the primer off with 320 grit, wet. This allowed me to quickly knock down the primer to a good smoothness. Got rid of all the pits and dimples that are inherent with an off the shelf rattle can type of paint.
Here's how it looked as I began tonight. Not really easy to see, but there's some swirling patterns from my sanding, and it's not all that reflective and smooth.
After an attack with the 400, and then the 600, I have this result. Note that the strap on the bottom is the completed one, with the 320-only sanded strap on the top. Again, sort of hard to tell the difference, but in person it's night and day.
The two straps took some time. Another trick is to dry the pieces off as you go along. It's hard to see any progress you have made while the thing is soaking wet, so keep a paper towel handy to wipe it down to see how you're doing.
The last part I tackled was the buckle. With all those curves and angles, it was a little more time consuming. You'll notice that there were a lot of burn throughs on this part, but that's totally cool, as those will totally disappear once it is molded. There's still some gunk left over on the buckle that needs to be wiped down with a wet towel before moving on to molding.
The last step, which I have not yet completed, it the final polishing. This is where you get a glass like surface. The trick for this is to use regular old Colgate tooth paste, and a nice soft sock. Yup. You read that right. It's a trick I picked up from Harvey Mudd college from a friend who had to build a screwdriver with a clear acrylic handle. The way to get that handle water clear was to go at it with a sock and some toothpaste. Hey, if it worked for a lab project at an engineering school, it'll work for a Superman Returns belt. I'm a UCIrvine guy myself, but I still think those Mudders know a thing or two :)