Chisel blades go blunt over time & can get damaged by nails or other hard objects.
To sharpen the chisel, you need whetstone or sandpaper of varying coarseness.
Here we have 3 grades, from roughest to smoothest: 240, 600, 1000.
Mount the roughest (240) whetstone in a vice or somewhere secure & wet with water.
Keeping the chisel level, rub the back of the blade until it is perfectly flat.
Repeat with the 600 then 1000 whetstone, until the back of the chisel is shiny.
A honing gauge attaches to the chisel & helps ensure a consistent angle while sharpening.
To set the gauge to the correct 25 degree angle, first draw a line 38mm from the edge of a scrap piece of wood.
Line the edge of the chisel up with the line on the wood & tighten.
Moving back to the roughest 240 whetstone, sharpen the chisel ensuring it is flat against the stone.
When the edge is flat & the angle is even, repeat its the 600, then 1000 whetstone until the blade is shiny.
Draw a second line on the wood, this time at 30mm for a 30 degree angle & line up the edge of the chisel against it.
Sharpen with the 240 whetstone again, but this time only take off a small amount, to create a super sharp second edge.
Repeat with the 600 & 1000 whetstone, until the blade is shiny & sharp.
The chisel is not ready to use.