Chip out the plaster with a steel chisel.

【chip】用钢凿子铲掉那些灰泥。

Our best steel chisels are made on the same plan: at the cutting edge they have a thin plate of hard steel, which is supported or backed up by a thicker plate of softer steel.

刀口由坚硬的薄钢片制成, 后面再附上一块更厚的软铁。