Any way to preserve the stones?

I tried to save a few stones from my last flush because they were very big, but they didn't seem to keep well. Since they were soft, I couldn't really clean them well. I just put them in a jar with air ventilation hoping they'd dry out. I checked on them today and they ...well... didn't look like something I'd want to show anyone. Most of them kind of dissolved and there was kind of an crude oil look on the bottom of the jar. I saw on the Liver Flush page some nice preserved stones. Is there a way to clean and save them for future reference?

thanks,
Perry