Increase in Bone weight

[Zartasha]

Dear Support.
I am trying to dry the bones up from the last 3 weeks in an open air but withing laboratory mainted room temperature. For continuous two weeks, the bones were losing weight. I measure them on digital physical balance.

On the 3rd week I started noticing gain in weight. I put the bones (femurs of birds) in a sealed plastic bag to see if it works or not as moisture could be the first thing that came to my mind. However, they are still gaining weight.

Anyone who know why is it happening? Thanks

Zartasha