For me the period between the two world wars ( Interbellum ) is the strongest for Peter Alma. In these years he made his most important works. Communist and artist at the same time, he was very much influenced by the socialist and communist art from the early decades of the 20th century.
Among his friends Hildo Krop, Berlage and Charley Toorop. Unfortunately he never became the famous artist he would have deserved to be. This means that his (graphic) works can be bought at very reasonable prices and at auction you can become outright lucky for some 50 Euro or so. I compare his graphics with the best Gerd Arntz made in his prime and beside their artistic value these works belong to the strongest graphic works from then first half of the 20th century.
http://www.ftn-books.com has the Stedelijk Museum Alma catalogue available.
BTW. the above catalogue was designed by another great from last century. Piet Zwart did the design.