| 摘要 |
A paper sheet, preferably 45 or 60g/square metre, is incompletely transparentised by treating it either with a xylene solution of polystyrene and kerosene or with a carbon tetrachloride solution of the agent specified in U.S.A. Specification 2,616,815 so that the gas permeability is below 50 seconds and that the reduction in exposure time is at least 50% of the maximum attainable reduction. |
