When an asset is revalued, the gain on revaluation (i.e. the new value less the (cost – accumulated depreciation)) is credited to the revaluation reserve account, which is not distributable as dividend.
As the revalued asset is depreciated, the excess of the depreciation on the revalued amount over the depreciation on the original cost is transferred from the revaluation reserve to the retained profits because that amount does now become distributable.