How are latent fingerprints formed? Our fingers have a very slight amount of moist acid that is necessary to hold objects, and the acid makes an impression on many surfaces. The fingers are always moist with small levels of perspiration, which, when dried, leaves an impression much like a drinking glass will leave a ring on a table. The ridges on the fingertips press into the surface of a table, doorframe—even glass. The oils that are on the skin transfer to the solid surface on which the fingerprint appears.