Since I had a few people asking about it, figured I'd create a quick post on how to get a nice glossy finish. There's no secret to it really, just a bit of work. Don't expect to just spray something out of a rattle can and have a nice surface when it dries. However, a tip that may save you some frustration, is to finish a test piece to completion before doing anything to your actual project. If something goes wrong along the way, you'll find out then, and you can just throw out the scrap and start over. Also, don't spray solvent based paints on top of water based. If you do something like this, you'll be glad you did it on a test piece and not your final work.
Standard disclaimer: Before you start, you should have a respirator and eye protection at minimum. Solvents and other paint chemicals are not something to take lightly.
Step 1: Get your surface prepped. It needs to be flat. Best bet is blocking it flat up to like 600 or 800 grit. If you're going for a piano black, just make sure your surface is well coated. You can prime first if necessary.
Step 2: Clear coat. This is the important part. The better clear you use, the better it will look. High build is the key for a deep glossy finish. I use an automotive 2K polyurethane. This is dangerous if you don't know what you're doing. If you value being able to breath, you need to use a proper respirator and have ventilation going. There are plenty of clear coats you can use, with different kinds of applications. It doesn't really matter as long as you can sand it. If you're clear coating wood, make sure you've sealed it first.
Step 3: Sand. Block flat. Start with 800 grit if your surface isn't too bad. Do not move on until your surface is uniform. No peel or craters should be present. The surface should be completely uniform before moving on. This is key. Anything you mess up here will be in the final surface.
Step 4: Sand more. Use 1500 to remove all traces of the scratches 800 left. If you don't, you'll see them when you're done. Your clear should be a bit less cloudy after this. You can move onto 2000 if you want, but if you have a mechanical polisher, it's not necessary.
Step 5: Rubbing compound. This is much easier mechanically than by hand. Spread compound on your panel, not so that it's soaked and you're tossing compound everywhere when you hit it with the pad, but enough to cover it. This is going to get rid of all the scratches in the last step. However, this will leave swirl marks. I use a foam pad for this.
Step 6: Glazing compound. This will get rid of the swirl marks in the last step. Use a different pad here, no cross contamination. Make sure your surface is clean before starting this.
Step 7: Cleanup. Use a soft rag to wipe off the rubbing compound. You can then hit the surface with some windex or something and wipe it down with a rag. Paper towels will leave very light scratch marks, so use a soft rag.
Here are some pics of the last project I worked on.
Primed. Sand to 400 after.
Painted. If flat, no need to sand, otherwise sand to 600-800
This is the clear I used, as well as the sealer on the veneer. Spraying this type of 2K poly is dangerous if you don't know what you're doing. If you don't have experience, use something else. You need to seal and sand up to 600-800, otherwise the wood will soak up the clear. The clear will sink into the grain depending. Not a big deal, just block it flat to 600-800 and spray more. You could always fill the grain with grain filler instead before sealing. I prefer having the depth of the grain in the surface, so no filler here.
This is in the middle of blocking. You can see some low spots. There should not be any before moving on.
This is what the veneer looks like during sanding after the clear coat. Block it nice and flat.
Keep sanding up to 1500-2000. This is at 1500. If you don't have a mechanical polisher, sand to 2000.
Now it's time for rubbing compound.
Here it is after rubbing compound.
Next up glaze. There will be some swirl marks left after the rubbing compound. This will clean that up.
And this is what it looks like with black.
And finished product.