I was asked recently, "how do I know when a painting is finished?" Answering with "I just know...they talk to me" was a bit glib, so I gave this question a bit more thought.
Paintings do let me know they are finished or nearly complete. Not verbally of course, but they speak to me in other ways. It is often when there aren't any areas that are awkwardly sitting there on the surface of the canvas or jumping out like dogs balls when they are not supposed to. It's complete when I go to add a bit of this here and a bit of that there, but come to realise it doesn't improve the overall look any more and if I'm not extra careful, this is where the painting can loose it's purity and essence by being overworked.
If, I feel there is a major change that needs to happen then I leave it for a day or two and come back to it with a fresh mind and clear eyes. On the other hand, I can think a painting is finished and I come back the next day to find that it clearly is not and wonder what on earth I was thinking the day before!
It is like a dance at the end. I make a move, then the image responds. I mostly looking for balance and contrast between light/dark, textured/ smooth, active and restful areas, hard edges/soft edges etc in the overall image.
As I prefer not to work from a fixed subject or image, it means the whole painting is being created from my memory and life experiences. Ultimately it is from that place only, that I will know if I have resolved what I first set out to achieve. It is always a challenging stage of the creative process and I have learned the most by making many mistakes. I've developed a lot of patience along the way and I try not to rush things through just because there is a deadline. If I can't complete the work to my satisfaction and the deadline is looming it is better for me to pull out that work from the exhibition, if at all possible rather than madly force through to an unsatisfactory and un-resloved ending. High pressure deadlines are for the very experienced and seasoned artists. I will have to get used to them eventually, but not while I am still learning so many other new things to build my art career.
So, my experience, up till now has taught me to take my time, be committed, show up daily to your work even when it goes pear shaped, practice, practice, practice, don't bully your artwork, be gentle, stand back and look and wait for the artwork to speak to you, love it, nurture it and journey with it to the finish. In the end you want your work to speak to the viewer, so it needs to speak to you first of all. If it doesn't, then let it go!