They could have been enlisted privates (mostly peasants in 1914 rural France), blacksmiths (present in most villages), metal workers, mechanics, and even jewelers, all could have contributed to these creations. Therefore there is a broad range of designs, depending on the individual artists.
This activity would take place in the rear lines of the trenches network (the noise of hammering would have been far too dangerous closer to the enemy lines). It became to be a good antidote to boredom and homesickness for the soldiers. Soon workshops and Rehab Centers would harbor this lively activity. P.O.W. could survive bartering these artifacts for food and other goods.
Production included smoking (lighters, ashtrays, match boxes, etc..) and writing materials (pencil holders, ink stands, paper weight, etc…) also picture frames, miniatures airplanes, submarines, and tans.
Shell commemorated a date or a place or a battle, they also could be dedicated to a parents or sweethearts . Very few are signed as shells were property of the army and meant to be remanufactured and reused.
In France, vases in pairs would adorn mantelpieces and be polished often. Tarnished shells would be viewed as a sign of neglecting the household and the absent soldier.
Trench Art grew as a cottage industry, attending the families of deceased and Units waiting to be sent home.
It played a vital role for the rebirth of the local economy. In the US, ammunition surpluses were turned into commemorative items.
As time went by, those items lost their sentimental value, and would be devalued as decorative objects put away in attics, garages, barns. But nowadays their historical value is more and more recognized. They provide a vivid link to our past and make it less abstract