Sources
The advice here is reworded and combined from general art teaching, not copied. These are good places to read further. They are a general reading list, not page-by-page citations, and the links go to the publishers themselves.
- Posemy ArtPosemy Artvisit
- ProkoProkovisit
- ArtwodArtwodvisit
- London Art CollegeLondon Art Collegevisit
- Eckersleys Art & CraftEckersleysvisit
- Watercolor AffairWatercolor Affairvisit
- Golden Artist Colors technical resourcesGolden Artist Colorsvisit
- Winsor & Newton Art AdviceWinsor & Newtonvisit
- Wikipedia: DrawingWikipediavisit
- Wikipedia: Perspective (graphical)Wikipediavisit
- Wikipedia: Fat over leanWikipediavisit
- The Met Open AccessThe Metropolitan Museum of Artvisit
Estimates such as difficulty, how common a mistake is and the time a fix takes are our own judgement from several of these sources, and are marked as approximate on each page. If you spot something wrong, the about page says how the pages are made.