I claim the ornamental design for an expanding corner for an art canvas frame, as shown and described.
FIG. 1 is a perspective view of an expanding corner for an art canvas frame, showing my new design;
FIG. 2 is an enlarged perspective view of FIG. 1;
FIG. 3 is a left-side elevational view of FIG. 2, the right-side elevational view being a mirror image thereof;
FIG. 4 is a top plan view of FIG. 2, the bottom plan view being a mirror image thereof;
FIG. 5 is a rear elevational view of FIG. 2; and,
FIG. 6 is a front elevational view of FIG. 2.
The broken lines showing a canvas frame corner in FIG. 1 depict environmental matter and form no part of the claimed design. The remaining broken lines represent portions of the expanding corner for an art canvas frame that form no part of the claimed design. The dot-dash type broken lines represents a boundary of the claimed design.