Department of Agro-Industrial Biotechnology , Maejo University Phrae Campus Rongkwang, Phrae 54140

Study of color quality and indigo content of indigo plants in Phrae province to improve the quality of the indigo dye fabric. The samples of indigo plants group in various areas of Phrae province include Hom’s large leaves from Ban Na Khu Ha (Strobilanthes cusia), large-leaves Hom from Ban Mae Lua (Strobilanthes cusia), Hom’s large leaves from Ban Na Tong (Strobilanthes auriculata voucher.), Hom’s small leaves from Ban Na Tong (Baphicacanthus cusia voucher.), Hom’s large and small leaves from Phrae Research and Development Center (Strobilanthes cusia and Strobilanthes auriculata), Indigo (Indigofera tinctoria) from Ban Pha dam and Java indigo (Marsdenia tinctoria R. Br.) from Kaew Wanna Shop. were collected. The results of quantity of indigo found, the large leaves from Ban Na tong showed highest of indigo plaste at 8.9701 grams per 100 grams. The color quality of indigo plant extracts in Phrae province
found that Hom from Ban Mae Lua demonstrated great in color quality with the mean brightness (L *) at 59.70 and the mean of green intensity (a *) at -5.29 and the mean of blueness (b *) at -0.40. The comparison of natural dyes in each source with chemical indigo dye were showed natural indigo has better color quality than chemical indigo dye.