What do you do with those old paintings that end up in a mess and clearly have not worked? Turn them into paper darts? Use the backs for another painting? Frame them and give them to your least favourite aunt for Christmas? Whatever you do, don't tear them up or throw them away as they are more valuable than you may imagine.
If you keep your old 'failures' in a folder the time will come when you will find them extremely useful to practice techniques. In this scene of Tideswell Moor in the English Peak District you will see a dark cloud on the left with a rain squall beneath it. This was achieved with a glaze - a transparent wash laid over an already-painted part of the composition, once it had completely dried. In this case it was done by wetting the paper first so that a soft edge would be achieved on the falling 'rain'.
Most inexperienced artists find this glaze technique rather daunting, and of course it is easy to mess up an otherwise competent painting. In order to gain practice with this technique there is nothing better than to do it on your old 'failed' paintings. You have nothing to lose and you might end up with a really good painting after all. The glaze method can be useful for warming up or cooling down a painting or an area within that painting, or for creating shadow or falling rain as in this case where you wish to suggest a film of atmosphere in between the viewer and part of the composition. Have fun with your old paintings!