On my own journey towards mastery I'm sharing the resources I find useful. Some artists hold their trade secrets close to the breast, fearing others may surpass and outshine them. I know that this will be a long journey and am glad of like minded companions willing to travel with me when our paths converge for a time. And I don't believe when a compatriot shines I fall into shadow. I prefer to believe we can bask in the reflected glory of our friends' success making each of us a little brighter.
So in the high spirits of setting out on an adventure I'm sharing a link to Harold Speed's The Science and Practice of Drawing. It's conversational and entertaining and it may not make the journey to becoming a true master any shorter, but it does give us signposts to keep us on the true path.
Speed's book The Practice and Science of Drawing falls in the public domain and is available as a free download from gutenberg.org