| http://www.w3.org/ns/prov#value | - Voids in microspheres of the invention are desirably avoided, i.e., by firing the gelled precursors to a dense state, to improve transparency, to avoid the weakening effect that structural gaps can cause, and to avoid absorption of moisture or other liquids that can degrade the microspheres, e.g., through freeze-thaw cycles.
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