This study was conducted to develop an effective mordanting method for black color expression of silk and cotton fabrics using the neutral extract (NE) of Pinus radiata bark and various iron mordants. Also, mordanting characteristics of iron salts in equimolar concentrations were evaluated. The mordanting was carried out in methods of pre-, post-, and pre- and then post-mordanting in one process with ferrous sulfate (FeSO 4 ), ferrous chloride (FeCl 2 ), ferrous acetate (Fe(CO 2 CH 3 ) 2 ), ferrous lactate (Fe-lac, Fe(CH 3 CH(OH)CO 2 ) 2 , ferric sulfate (Fe 2 (SO 4 ) 3 ), and ferric chloride (FeCl 3 ). The mordant concentration was 1 mM o.w.f. (on the weight of fabric); 0.5 mM for Fe 2 (SO 4 ) 3 . The colors of mordanted silk fabrics ranged from dark brown to black and that of mordanted cotton fabric were in the range of light grayish-brown to gray. Using ferrous ion (Fe 2+ ) and post-mordanting methods led to the expression of darker colors and the divalent and trivalent cations (Fe ions) were found to influence dark color expression. The color of silk fabric in the presence of the combination of Fe 2 (SO 4 ) 3 pre- and Fe-lac post-mordanting (PSPL) was closest to the silk fabric dyed with synthetic black dye. Based on the colorfastness assessment, an increase in the light fastness of PSPL silk fabric was observed along with a decrease in the rubbing fastness compared to the non-mordanted silk.