I don't think it's your rendering per say, what type of markers are you using ? If you want to work in layers, and being able to blend, alcohol based markers work best, you can find very affordable ones to start with on internet or probably your local art store, you can choose between brushtip or ballet tips, and they often come with bigger, "chisel" tips. What's good with these markers is that they don't dry immediatly, so you have time to blend them, there's ton of tutorials about them online ; then you can work on rendering realistically once you have the right material :) | Artwod Feedback