A student paints a large acrylic canvas in an unheated studio in January at about 5 degrees Celsius. In March the film is chalky and lifts under a fingernail. How does the way acrylic dries account for the failure?

B. Being below the minimum film-formation temperature stopped polymer particles from coalescing.

Coalescence has a temperature floor, commonly quoted near 9 degrees for artists' acrylics, and below it the particles never fuse however long the water takes to go. The film is then loose pigment held by almost nothing. No amount of extra drying time repairs it, because the process that failed is physical rather than chemical.