Standardized evaluation method of tinctorial plants – the case of Punica granatum

CRITT Horticole is one of the pioneers that reintroduced dye plants cultivation at commercial scale and optimized dye molecules extraction. Since then, we have been searching for new tinctorial plants to expand our knowledge in natural dyes and transfer it to our customers. For that purpose, we evaluate plants from our own crops and plants from various geographical origins on request of international partners. As an example, we received dried pomegranate peel (Punica granatum) from Tunisia, and we were asked to evaluate if a dyeing extract could be obtained from this material and be used for textile and hair dyeing. To do so, we applied a standardized method that we developed to assess the colour potential of various plants. The first step was to study the biochemistry of the plant, we identified dyeing molecules and ensured that the plant is non-toxic according to the literature. Then we performed maceration with a natural solvent, we concentrated the liquid extracts by rotary evaporation and then dried them using a hot air oven or by freeze drying. The dried extracts were milled and extraction yield was calculated. Once we had obtained the extract in powder form, we performed a colour evaluation and fastness test of the plant extract. To characterize the colouring power of the extracts a spectrophotometer analysis was done from 200 to 800 nm. To evaluate the dyeing properties of the extracts, we dyed silk fabric pieces under precise conditions (generally Alum 10% WOF + Extract 10% WOF). The dyed fabrics are submitted to a lightfastness test using a suntest. In addition to textile application, we performed natural hair dyeing. Lastly conclusions on the extract were established by comparing yields, colour results and fastness with those of other well-developed extracts from our range of extracts. Extraction yield and lightfastness were satisfactory but the colours obtained both on silk and hair dyeing were disappointing as the colour was not very intense. However, tannins from Punica granatum could be useful in the hair dyeing industry to make natural dyes such as henna last longer.