Unusual WW1 Dated 1917 German Trench Art Shell Case

This is a most unusual WW1 trench art shell case for a number of reasons, firstly the base is made from steel, towards the end of the war brass was getting scarce so steel was used wherever possible, secondly the decoration on the outside has a central picture of a Medieval lady with full headdress (I am thinking possibly a saint) below this 'Boilleux Somme' I assumed the Boilleux was a place but I cant tie it down the closest I get is that it is a family name rather than a location. The base due to the steel has rusted but you can pick up the Sp61 Spandau mark and the date for 1916. It comes in very good condition and stands 9 inches high.