It would hardly be proper to festoon the Ashmolean’s exhibits with Christmas decorations. So what to do? Luckily an answer was at hand: stage a seasonal OSJ Prom, featuring the OSJ Ashmolean Choir singing Christmas music a cappella.

Each half of the concert was bookended by a different setting of O magnum mysterium, “O great mystery and wondrous sacrament, that in a humble crib the ox and ass should see our Lord.” Beginning with Byrd, each setting built the mystery from a gentle beginning. Later settings were by Poulenc, Mendelssohn, and finally the American composer Morten Lauridsen: his contemporary treatment of the text sounded particularly telling.

Conductor John Lubbock filled his two O magnum sandwiches with a wide variety of further Christmas offerings. There were lullabies like Hush my Dear, Rocking, and The shepherds cradle song. In contrast, there were dance-like carols such as David Willcocks’s always delightful arrangement of Tomorrow shall be my dancing day.

Several carols had been arranged by John Lubbock himself, often using a solo line of text sung above a wordless choral backing — Tannebaum/Silent Night was particularly effective. Lubbock also sung one or two of the solos, a reminder that he was once a member of the Swingle Singers.

But the stars of the evening were the members of the OSJ Ashmolean Choir. This group was formed for October’s OSJ Prom, and I was struck at the time by the integrated sound it had already achieved. That impression was confirmed this time around, with the even balance between the four vocal parts showing to advantage in carefully constructed pieces like Bruckner’s Virga Jesse Floruit. Once again the Ashmolean atrium came up trumps acoustically, with only the very softest passages needing a spot more word projection.

This was a heart-warming end to the highly successful first OSJ Proms season — six new Proms have now been announced for 2012.