Okay, you asked for critique, so I'll give you some, I'm just going to be honest. - The fat black outlines are sorta ugly, I just don't think they're necessary. Maybe 1x1 line of black, but not that much. - There's very little detail, I opened the red gem up in Gimp and zoomed all the way in and could hardly see the shadings. - It doesn't really look like a gem, it's flat-ish.
BUT! I'm not going to leave you at that, I'm going to actually help you. As I said, I took it into gimp, and I made it look a bit better. What I did to improve it - Trashed that black line - Added some reflections - Added 3D sides, to make it look 3D. ~~~ I hope this helps!
1. You asked for constructive criticism. Oak gave you some. Did you not like CC? You didn't respond. Just wondering. 2. I do think your drawings are flat. The gun is nice, there's some detail, but again, like Oak said, there isn't enough shading for it to look more 3 dimensional. 3. Not all gems are rectangular. Make some circular ones! Or diamonds!
1. You asked for constructive criticism. Oak gave you some. Did you not like CC? You didn't respond. Just wondering. 2. I do think your drawings are flat. The gun is nice, there's some detail, but again, like Oak said, there isn't enough shading for it to look more 3 dimensional. 3. Not all gems are rectangular. Make some circular ones! Or diamonds!