Sharpening your Global knives is strongly recommended by Whetstone sharpening. The Global factory have specifically designed the Minosharp whetstones to re-create the way the knife was first made and so that when you re-sharpen your knives you can re-gain that super sharp edge.
Click here for a list of the Whetstones available.
If you prefer to sharpen your knife using a steel, Global do have a ceramic and diamond steel available. However, these should be used more to hone the edge as opposed to fully sharpening the knives.
Through use of your ceramic steel, residue can form which is a silver/grey colour. This is a normal occurance and one that shows you are doing the right thing! But it does mean that the pores in the ceramic rod are being clogged up and the steel will be less effective.
To minimise the clogging on your ceramic rod, please wash it in warm soapy water regularly. You may also need to use a scourer.