Soap 1: Before
Soap 1: After
Soap 2: Before
Soap 2: After
Here are some things I have considered:
Rancidity of the oils: The sesame seed oils of these soaps are from a different batch and both from the reputable supplier that has always delivered top quality oils. Therefore I think that the oil quality is not the cause for this.
Rancidity of the soap: Both soaps have been properly stored in a cool, dark and dry place. There is no scent of rancidness in either one of them. The change of color happened quite soon, about 10-12 weeks after the soap was made. Also, the color change does not look like soap gone bad.
Discoloring EO: The essential oils in Soap nr. 1 are palmarosa, rosewood and lemongrass. Soap nr. 2 is scented with bergamot, mandarin, coriander, sage, lemon, grapefruit and marjoram EO. The only thing common in these two EO blends is a high content of linalool.
Right now I'm pondering two options. Does the sesame seed oil itself make the soap change color? Or does linalool somehow react with the sesame oil causing this... Any suggestions?