The impact of impregnation and bleaching on the hardness of varnish layers on oak (Quercus petraea L.) wood was investigated. A number of solutions [sodium hydroxide (NaOH) and hydrogen peroxide (H2O2); NaOH, calcium hydroxide, and H2O2; NaOH, magnesium sulfate, and H2O2; sodium bisulfate and H2C2O4 (.) 2H(2); sodium silicate and H2O2; and potassium permanganate, sodium bisulfate, and H2O2] were applied at a concentration of 18% to bleach both impregnated [Tanalith-CBC (T-CBC) or Imersol-WR 2000 (I-WR 2000)] and unimpregnated (natural) wood panels. Subsequently, a water-based varnish (WB) was coated over the samples, and the hardness of the varnished layers was determined in accordance with ASTM D 4366. Among the samples that were varnish-coated without bleaching, T-CBC/WB yielded the highest hardness (59.50), whereas I-WR 2000/WB exhibited the lowest (49.17). However, among the samples varnish-coated after bleaching, the highest (56.50) and lowest (40.83) varnish hardness values were obtained with T-CBC/solution 2/WB and I-WR 2000/solution 4/WB, respectively. All the chemicals used for the bleaching process reduced the surface hardness. However, after the varnish coating, except for solutions 4 and 6, all the solutions showed hardness values similar to those of varnish-coated natural (control) samples. (C) 2004 Wiley Periodicals, Inc.