If you are registered, you get access to the members only section, can participate in the buy & sell second hand forum and last but not least you can reserve your preferred username before someone else takes it.
I haven't exposed it to sunlight, so I cannot answer if it darkens. There were several patches of a darker rust color on the sides of the yellow coticule when I got the stone. Out of curiosity I lightly sanded them to see what would happen - the sanding removed the rusty color. The last shot of the "toe" shows a tiny spot of the rust color where the coticule meets the BBW. And yes, the slurry on this stone does have a more slippery/soapy feel than my La Dressante or Les Lat.
This stone also came with much more rounded (softer) edges and corners then other stones I have purchased, which I find curious Note: it does have one straight side because I trimmed the width down to 40mm with a hacksaw and haven't had time to round out the cut side to match the rest of the stone.