Historical and archival research focused on the Portuguese Inquisition documents (1551–1800) uncovered the use of arena known as blotting sands, a writing accessory used to hasten ink drying. We present in this work the first systematic study combining image analysis, SEM/EDS and µ-Raman techniques, statistics and chemometrics to characterise the blotting sands used by the Portuguese Inquisition and hypothesise their provenance. Iron-titanium and iron oxide minerals categorised as texturally mature sands are the dominant species, consistent with sediment extraction from fluvial or beach contexts and later processed. Chemometrics unveiled time period trends by clustering the samples according to morphology and composition data. This work constitutes a groundbreaking step towards uncovering this intricate writing tool.PTDC/ART-HIS/32327/2017; UIDB/04449/2020; UIDP/04449/2020; LA/P/0132/2020, UIDB/00057/2020; SFRH/BD/147528/2019; PTDC/ART-HIS/32327/201
