In the late 1700s, acid was accidentally spilled on the upper right side of the cloth. In 30 days, without any treatment, the damaged material was miraculously reconstructed.
This is half true. In 1795, nitric acid was accidentally spilled on the left side of the Image. There is still a trace of the spill. Thirty-five years later, in 1820, the accident was written up in a notarized report, which stated that nothing happened to the cloth. (In actuality, there is a subtle stain that is visible to the naked eye, especially from the back of the Image).
So while it’s false to say that the fabric was miraculously reconstructed in 30 days, it’s still amazing that the acid did no significant damage, either to the Image or the fabric itself. (Cf. Instrumento Jurídico sobre el agua fuerte que se derramó, casualmente, hace muchos años, sobre el Sagrado lienzo de la portentosa Imagen de N. Sra. de Guadalupe de México, 1820, AHBG, Correspondencia con el Supremo Gobierno, Caja 3, Exp. 54).