Ok, you have done a lot and you have some very nice artwork.
Time to tweak your website:
-Title your pages, 'index' just wont cut it. Consider Art by Magicpallete or Acryllic Art by Magicpallette. Your other pages need a more descriptive title too. Keep them short.
-On NavBar, use a smaller font (I see Arial) so that the categories don't overlap with the design ends. Might also want to add the link behing the bar not just the ends.
-PayPal has other options for the buy now buttons. "Add to cart" is a good one, see
here and looks professional.
-The LightBox works fine, however your site would benefit from seeing these images enlarged to the roughly same size. Some take up more than one page, others open to about 2x2 inches.
-On images look for Collectors' posts on images, some of them are pretty large and this could cause delays in loading.
Good luck.