Used cotton blotter sheets. (I am downsizing my studio!)
Sold in packs of 10.
Sizes are approximately 18 x 24 & 23 x 30 (variances in dimensions should be expected around 1").
*The 18x24 appear to be a bit more used than the larger. They are sold as is so do not be surprised if some have leftover coloration or slight stains. They will still do the trick as absorbent paper.