The ornamental design for a double-sided clear writing slate and base, as shown and described.
FIG. 1 is a top perspective view of a double-sided clear writing slate and base showing our new design, the lid of the writing slate being in a closed position, with a removable writing template inserted therein;
FIG. 2 is an inverted, perspective view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 is a right side elevational view thereof, the left side elevational view being the mirror image thereof;
FIG. 5 is a front, facing view thereof;
FIG. 6 is an inverted, back facing view thereof; and,
FIG. 7 is a top perspective view thereof in which the lid of the writing slate is in an opened position.
The broken lines showing lines and boxes of a writing template in FIGS. 1, 3, and 7 are included for the purpose of illustrating environment and form no part of the claimed design.