What makes dyes used with harakeke change colour? Levels 3 and 4
Aim
To understand that when dyes are mixed with different substances they result in either permanent or reversible changes in colour.
Why does hīnau dye turn black?
Hīnau contains a lot of tannin. Tannin combines with iron salts from special mud, sometimes known as paru, to make a black iron-tannate dye.
What makes tanekaha dye turn red-brown?
Tanekaha turns reddish brown when rubbed with ash. This is because the ash contains potassium carbonate which causes the dye to change colour. Potassium carbonate is a base, which is the opposite of an acid. When acids and bases are mixed, they cancel each other out and are no longer reactive.
The reddish brown tanekaha dye can be changed back to brown by adding acid.