def atomBareSymbol(smbl):
    """Remove atom type string stripped of isotope and ion charge symbols.
    This removes blank and leading [0-9-] or trailing [1-9][+-] characters.

    smbl -- atom type string such as "Cl-", "Ca2+" or "12-C".

    Return bare element symbol.
    """
    rv = smbl.strip().lstrip('0123456789-').rstrip('123456789+-')
    return rv
