Strange friends....

My watercolor sketch today is from a photo I took last summer of a discarded small boat motor leaning against a flower bed post and its "visitors" LOL.  I always wonder when I see the sunlight dazzling off something - if I try to paint that how do I KNOW visually, that it is the sunlight making it look like that...other than assuming because the sun is out that's the source...what are my visual cues? and then trying to translate that into not only painting but any kind of creative project....how do we create light effectively in a 2-D world...? Light is a mysterious friend!!