6000 Grit Water Stone
HNT Gordon recommend and sell Japanese waterstones. After your initial sharpening on the 1000 grit stone, to finish the job you will need to refine your edge by honing it on a 6000 grit stone shown in the photo.
Stone Size 210 X 70 X 20mm
The instruction leaflet Sharpening Process will come with the stone and details the full procedure for sharpening your blade.