Through-thickness/through-time composition analyses were made onREBa2Cu3O6 + x (REBCO) films prepared from metal–organic deposited (MOD) precursorson a RABiTS (rolling-assisted biaxially textured substrate) template.Y Dy0.5Ba2Cu3O6 + x films were fabricated either by a single precursor coating or by two separate, equivalentprecursor coatings with an intermediate decomposition. Specimens were quenched atselected times along a heat treatment profile that simulated conditions used byAmerican Superconductor, then examined by Raman microscopy along mechanicallymilled slopes through the REBCO films. Upon reaching the reaction temperatureTR, the precursor initiallytransforms into a (Y, Dy)2Cu2O5, CuO, Cu2O, and RE–Ba–F–O phase mix, and this is followed shortly by substratelevel REBCO formation that propagates upwards through time. Our resultsindicate that (1) the single layer (SL) and double layer (DL) films (both ∼ 1.2 µm thick) react to completion at about the same rate and arrive at a similar final compositionand (2) some residual Ba–Cu–O phases persist near the top of the fully reacted films. Theperformance of the SL film was moderately better than that of the DL film, seemingly dueto better through-thickness REBCO texture as determined using x-ray diffraction.