Oil paint on linen

[Dan Howard]

Shields were meant to be used in battle. The facing will need repair after every battle and it was further damaged in the field by wear, mud, water, and blood, so it didn't really matter whether linseed oil degraded the fibres. If you want to use the shield for a non-period purpose (e.g. keeping it on display for an extended period of time) then you may need non-period materials.