I'm working into the main body of the jug, trying to get the gradations smooth between the light and dark. To do this I have mixed colour strings of nine tones of three different mixtures, one using ultramarine and burnt sienna with a bias of burnt sienna, another using the same colours but with a bias of ultramarine and the third using the same colours but adding raw sienna. To make colour strings you start at white and then keep adding the other colours until you have nine different tones of the same mixture of colours, the final tone having no white in the mixture. This is very useful when you want the same tone but a warmer or cooler colour so that you can alternate between warm and cool tones to give body to the object.