Complex sentence: The pattern of discolouration was very clear when the shield was recovered from the River Witham (see 1863 drawing below), but although it is still possible to see the discolouration under certain lighting conditions, the boar design is no longer easy to make out.
Split into simpler sentences: The pattern of discolouration was very clear when the shield was recovered from the River Witham (see 1863 drawing below). Although it is still possible to see the discolouration under certain lighting conditions, the boar design is no longer easy to make out.