Mochiko is a high-gluten rice flour used in rice paste resist. Before ordering from me, be sure to check locally–your corner grocery store may carry it! The photo shown here is of mochiko made in California and produced by the Koda Family. It's often available in large grocery stores or specialty gourmet shops.
An alternative would be any short grain (pearl grain) rice milled into a very fine flour. Many cultures produce this. It is sometimes known as sweet-rice flour because of the high gluten content.
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I also conduct a full range of natural dye and katazome paste resist programs via Zoom and in person. Be sure to check out my workshop page or sign up for my newsletter to be the first to find out!