This is the dataset used for calibrating the SPAD camera timing skew and to generate an instrument response function for the microscope. This dataset is an input to the MATLAB SPADlinearization.m script. It was used in the preparation of the data in manuscript "Visualising Varnish Removal for Conservation of Paintings by Fluorescence Lifetime Imaging (FLIM)". The measurement was obtained with a quenched fluorescein sample on a TCSPC microscope. The dataset is used to create calibration structures for the microscopic optical system. The calibration structures can be reproduced by running the SPADlinearization.m script on the raw data. The resulting calibration structure and the scripts are available in another dataset in this collection called "SPAD Linearization Code".