Looking for a better shine

Skip the weird organic additives, they are just things looking to cause trouble. The purpose of them is not to give a better shine, but to make the slurry more viscous so things don't bang around in the barrel and cause the stones to chip. The problem is that they invite bacteria or yeast to start fermenting the organic material, leading to gas build-up and stinky explosions. If you want to slow the action in the barrel, use something inorganic like plastic or ceramic pellets, or just cut back on the water so the grit-water slurry mix is thick enough to prevent chipping.

If you want a better shine -- make sure you tumble stones like agates that are hard enough to take a nice shine, only mix stones of similar hardness in the same barrel, do rough grinding until there are no pits or crevasses to trap grit and carry it to the next stage, wash barrels and stones scrupulously between grit stages to ensure no carryover of grit, tumble each stage long enough to remove the scratches from the previous grit stage (usually a week for the fine grind and the pre-polish stages, but longer if you have a lot of cushioning agent in the barrel), and run the polish stage for at least two weeks, three weeks is better, because you'll get a shine after one week, but a gleam after two or three weeks.

With a home tumbler, you should be able to produce results that put commercially-tumbled stones to shame.
-Don

Thanks to all of you who gave advice. It is much appreciated.
To clarify what I have done so far, I have been tumbling agates and other hard stones. The first batch came with my new 3 lb. Thumlers (purchased last Christmas as a present for my kids). The rest have been stones purchased from The Rock Shed - First a mixed batch, then amethyst. I also washed them between stages with Borax, having read this idea on this website. I generally go 2 - 3 weeks with the first stage, and then a week at a time with the rest, with the exception of the final stage. Generally, I check them in the final stage after 4 days and then go another week to polish. Of course when I start, the batch is 1/2 to 2/3 full in the barrel, but then it gets to about 1/3 full for the last stage. I use plastic beads as a buffer, but perhaps this is not the right source or I perhaps I don't use enough. Any further thoughts would be appreciated. BTW...

Randy, Love the Ronald McDonald video. Thanks for the input.
Rolling Stone - the shine on those stones puts me to shame.
Jack - Thanks for the link. It's also cool to communicate with someone from England!

Ahhh yes, the rocks definately won't polish if the barrel is only 1/3 full. Basically, the rocks are just getting beat up. Every time you check the rocks in the first stage, remove the ones that are ready for the second stage, put them in a zip-lock and replace with new rocks. When you have enough smooth rocks in the zip-lock, time to go to the next stage. Do this with each stage, always keeping the barrel 3/4 full.