Bookkeeper® Deacidification Spray (magnesium oxide in a non-reactive carrier with a surfactant) has recently been made commercially available for non-aqueous deacidification of paper artifacts. In a series of experiments, Bookkeeper® was applied by spray and brush to different papers and tested in a variety of ways to determine its effectiveness for the deacidification of small or individual artifacts. Atomic absorption spectroscopy, scanning electron microscopy, colorimetry and pH measurements were employed (before and after artificial aging at 90 C, 50% RH) to determine the amount and nature of the magnesium oxide deposit, and to assess the appearance and permanence of the papers studied. For comparison, some papers were treated with a different non-aqueous deacidification spray (Wei T'o™). Bookkeeper® Deacidification Spray was shown to deposit a significant amount of magnesium, penetrate the paper unevenly, leave a precipitate, and did not protect the paper from color changes during artificial aging.