Hello Michele,
I had worked with ivory in the past and do not think that freezing is a good option. If I were you I will inquire further with colleagues that are experts in this material. For example, make an initial search in find a conservator at AIC? and contact them to make further inquires. Are you sure that is ivory? What are the main characteristics of this material? a cross hatching (roughly diamond shaped cross hatching) is a good indication that the material is ivory, as are translucent wavy lines. You can write to me at
