Use a wire brush to remove any resin/deposit on the knife before sharpening.
A medium grade of carborundum stone which is used for knife sharpening.
The first operation is to clean the carborundum stone with a clean cloth to remove any dust or grit from the stone.
A small amount of very light oil is applied to the centre of the stone. Engine oil must not be used this operation.
Thoroughly rub small amount of light oil into the carborundum stone with a clean cloth.
Most horticultural knives of quality will have the manufacturer’s name on one side of the blade, as shown by the red arrow. The bevel on the blade is always on this side.
Maintain a 22° angle of the blade, this can be achieved by the finger and thumb holding the blade securely and safely. Only rub the knife blade against the stone in three forward movements, as shown by the red arrow, do not move the blade up and down on the carborundum stone.
Immediately after the three forward strokes on the carborundum stone, turn the knife over and gently remove metal deposits, which can be achieved by keeping the blade flat on the carborundum stone and gently moving it forward for 5 cm.
The knife should be able to cut through thin paper without any effort. A blunt knife can cause as many cuts to you as a sharp knife.