I always enjoy seeing healthy lithops in flower. Actually, I always enjoy seeing healthy lithops. Allain I have probably asked this before and have forgotten the answer, but what is the size of your square red pots? Based on the size of the Lithops schwantesii plants I'd guess they were about 8cm square. Very nice looking plants. Thanks for sharing.
I have various sized square pots. The one in the picture is 2 3/4 inch. I like to use BEF pots which have been popular with cactus growers in the UK for a long time. To me they have pleasing proportions. Hand made pots are seen less in the UK. The square pots allow more plants to be fitted into a limited space. I am not the only devotee please see http://www.hartley-botanic.co.uk/featured-blogs/lila-das-gupta/mystery-in-the-greenhouse-bef-pots