Frequently they embody materials which would otherwise have perished, but their transcription is, marred by an amount of conscious or unconscious falsification which seriously impairs their value.
The presence of these enclosed impurities impairs the transparency of crystals.
The estuary of the Dee is divided at its head by the peninsula of St Mary's Isle, but though the harbour is the best in south-western Scotland, the great distance to which the tide retreats impairs its usefulness.
Tannin is a hardening and astringent substance, and in large quantities impairs digestion.
When present in other metals, even in very small quantity, bismuth renders them brittle and impairs their electrical conductivity.