Tantalum films begin to crack and spall during vapour deposition on glass at a thickness of 180 nm. Islands and ribbons, 10 – 30 µm in size, delaminate by crack growth along the Ta/glass interface for several gIm after which the crack penetrates into the glass to a depth of 0.5–1 µm and complete spalling occurs. X-ray diffraction showed that about 50 % of the original bct, β-tantalum, phase had transformed to the bcc α-Ta phase. When Ta was deposited on glass that was first covered with 52 nm of copper, spalling was observed to begin at a thickness of 105 nm. In this case, the film first cracks and then peels along the Cu/glass interface and curls into scrolls indicating the presence of a small stress gradient. X-ray diffraction of the asdeposited film, and electron diffraction of ion-milled flakes, showed that Ta films deposited on Cu-coated glass almost completely transform to bcc α-Ta. The critical thickness for delamination along the Cu/glass interface is about 1/2 that for cracking in the glass substrate when an intermediate layer of Cu is not present. All of the above findings are in good agreement with previous observations on Cr films.