When "so that" has a comma before it, does it always mean a result? Normally it means a purpose without a comma.

ex)There are several Egyptian paintings of great interest preserved among the numerous other remains of Egyptian art in the British Museum......When the paintings were first discovered, however, their colors were as bright and pure as when they were first painted, because they had not been exposed to the influence of atmosphere. Red, yellow, green and blue, with black and white, were the colors employed. These were applied singly, so that no variety of tint was produced. ......