Museum officials have treated the work to make it suitable for display, cleaned it and fixed minor damage.
The painting features a view of a woman holding a child. The work was revealed on Monday. Stitches on a different painting by the same artist had attracted the attention of museum workers amid preparation for an anniversary Schjerfbeck exhibition.
Infrared scanning showed another image underneath the frame of a landscape of Raasepori, which was painted in the 1890s. The newfound work is signed by Schjerfbeck and it dates to about 1887.
The painting is now exhibited on the second floor of Ateneum side by side with the landscape which had covered it.