The photochromic properties of oxygen-containing yttrium hydride thin films are directly dependent on the oxygen concentration in the material. We use 16O/18O labelling to study oxidation of YH2 films. Oxygen penetrates the film through grain boundaries and intercolumnar voids oxidising the whole film thickness. without pronounced surface oxidation or self-passivation. https://www.mabelandfoxs.shop/product-category/swimming-goggles/