So the Henna questions just keep coming! Here is my theory on how the curl loosening effect works. Chai asks - 'Quick question: Is the possible loosening of the curl temporary? For example...would your hair return to it's normal state after one wash?'
This my theory based on the weight effect of Henna. I don't think that the effect is reversible given that Lawsone is a permanent dye. I believe the added weight is there to stay and changes in length would depend on
1. The amount of moisture in the hair (more moisture = more weight = looser curl)
2. The number of times you use Henna (more dye = more weight = looser curl)
Here is a diagram. For simplicity I have kept the hair in a wave shape. (Click the picture to get it larger, if you have problems reading, please let me know. )