2D Weightlifting Flour Sack - Colour

After sketching out all the inbertweens, I traced the line art (making adjustments when I needed) and coloured it in a light beige for the shade of the flour sack. I also did the line art for the boulder and coloured it in. As the shape is very simple and stays the same, I used the stamp tool to use the same line art for each frame, just moving them to the correct spot.

I then coloured in the flour sack, and on a separate layer drew over the boulder in the flour sack colour to make it appear as if it is over the boulder and lifting it up. I had the flour sack line art layer above all the other layers and erased it when it went over the boulder.

Afterwards, I added grass for the flour sack to stand on and for the boulder to hit. I then drew the shadows as if the light source was at the front and a bit to the right so the shadow of the boulder would cast over the flour sack. I am very pleased with the shadows, however I think the animation needs some work. In the first section, where the flour sack picks up the boulder, the line art appears to 'boil'. I had this problem throughout the whole process, so to correct I may have to redo the first part completely. I think the root of the problem was drawing all my inbertweens on my sketch layer first before doing line art. I also forgot to include the impact when the boulder hits the grass, so it looks like it's just resting on top. (which ruins the appearance of the heavy weight of the boulder)