Bird wings/Bat wings Drawing tutorial

I found a really good Bird wings/Bat wings tutorial that I would like to share

Index of Refraction

I tought I could start to post some references for anyone who want to shade properly. I'm still learning, but some techniques are the same.

It's very useful the have the refraction index with you. For those who don't know what is a refraction value, let me explain to you

In optics the refractive index (or index of refraction) n of a substance (optical medium) is a number that describes how light, or any other radiation, propagates through that medium. more