Agreed: this is a learning room here, not an art gallery!

Don't ever sweat the shadows, Dave. I've discovered by audience feedback that it's important to have a shadow in a drawing where there should be one, but accuracy is of secondary concern. IOW, your audience might look at a wrong shadow in a funny way, but they are more likely to notice when a shadow is missing entirely.

Besides, a shadow on a coarse diffuse surface? The detail in real life is barely discernible.

-g