>Hydrogen peroxide is an oxidizer, not a dispersant (disaggregant).<

Both peroxide and bleach (mentioned earlier) are oxidizers.  However, if there is a moderate to high level of organic matter or other reduced substances in the sediment (generally true of dark-colored sediments), then oxidizers may be effective at breaking up the sediment by dissolving some components and from the bubbles and heat released by oxidizing reactions.

Dispersants, like soap, disaggregate sediment by disrupting the attraction between sediment particles (or between sediment and you, your clothes, etc.) and by promoting water-dispersant-sediment associations.

Thus, it depends on the sediment type and how fragile the shells are as to what technique will work best.

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL  35487-0345 USA
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That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa