How can I deduce at what angle my knife should be sharpened against glass stone? First is to pay attention to the angle. Unless the knife is badly worn and needs some serious grinding, you should use a slightly steeper angle than the original edge.


Can you please indicate on my picture where &quot;the original edge&quot; is? What does &quot;original edge&quot; mean?



How do I calculate the &quot;original edge&quot;  of WÜSTHOF 4596-7/20 Classic Ikon 8-Inch Cook's Knife?  Do I need a protractor?

At what angle ought the knife meet my Glass Stone? Please specify a number.
The &quot;sharpening angle&quot; of a knife is the angle between the sharpening surface and the blade. The 'original edge' is the angle at which the knife has been sharpened previously. Sharpening at close to/slightly below this angle will make sharpening the blade easiest, as you don't have to work hard to change the angle (which requires moving more material from the knife).
I could not find any info on the factury angle for the knife you mention, but most Western-style chef's knives are sharpened at an angle of about 20 degrees. Note that this is a &quot;double-bevel&quot; knife, so the angle will be about 20 degrees on both sides of the blade. See for example this page for some graphics and more info.
The original angle is not something you calculate. Either you find reliable information from the manufacturer, or you have to somehow approach this angle by trial and error. A 'trick' that I've seen some knife sharpeners do is to 'drag' the blade over the sharpening stone, slowly decreasing the angle until there is a change in how much friction you feel.