Tumbling Stained Glass

I read various posts on this website and thought I could tumble stained glass. I volunteer with an organization that makes stained glass angels and sun catchers to raise funds for cancer research and patient care. Over $800,000 raised so far. We try to use all the glass but there are always small pieces left over. The smaller pieces are used for mosaics but having read the posts I thought we could probably raise more funds by tumbling the glass for larger pieces...maybe wreaths. More money raised means more research and maybe a cure. First I tried the "cool whip" container method. It didn't seem to make any difference. Next I decided to buy a double barrel rock tumbler. I was going to donate it to the organization since I didn't want there to be any cost to produce a new product. I cut glass into roughly 1 1/2" pieces, added water, a drop of detergent and builders sand. I've tumbled for four days and the glass don't look much different. Yes, the edges are a little less sharp but not rounded like sea glass. I've spent hours researching and a week listening to the tumbler run. I haven't used grit since the cost could be more than what we might earn and posts indicated sand would do. Before I declare this a hopeless project, what am I missing? Does stained glass ever get smooth without grinding the edges? Other volunteers were excited about the new project. Of course they want to work with the glass now and not wait until next year for a quantity of tumbled glass. I don't want to disappoint them but I don't know what else to try without purchasing expensive materials. I'm hoping someone can tell me if there is way to quickly tumble stain glass so the edges are rounded. Thanks for any guidance or suggestions.