Area measurement on cement samples

[sgarcia]

Hi everybody,

I am trying to make measurements along the circumference of a cement sample. The sample is composed by cement and a steel casing. What we do is put epoxy with a red dye between them. I want to measure the quantity of dye that there are there. I have been trying using threshold, manually and the automated threshold plugin but I am afraid that is not working because of the image quality, but I don't know how to improve it.

Any sugestion would be appreciate as I don't know how to fix it right now.

I attach a few examples of the photographs that I have. I took them with an optical microscope.






Thank you in advance, I hope to hear from you.