Which side of the strop?

Hi,

I've been lurking for a while. Reading the FAQ, watching YT videos and ordering loads of equipment.

I've now received a Whipped Dog razor and strop however I cannot find reference anywhere of which side to use. One looks the leather from a pair of brown shoes and the other is roughter and like suede. Which side is suppossed to be used for after shave stropping?

I know this is a basic question but I don't seem to be able to find the answer anywhere!

Thanks.