The pates on antique bisque head dolls manufactured by Kestner are made of a hard plaster and attached to the bisque with a much softer plaster.  The plaster for attaching can be softened quickly and easily with water without damage to the pate.

Get a cotton swab wet with water.  It should be wet, not damp.  Touch it to the pate just were it meets the bisque and let the soft plaster absorb the water from the swab.  Keep rewetting it and go around the entire pate two or three times, giving the water time to soak in.  

Let sit a few minutes, then carefully probe the pate edge with a small, sharp blade like an Xacto.  If you meet with resistance, repeat the wetting procedure and wait another minute or two.   

When the blade goes in easily, carefully and slowly work it around the pate, keeping the blade flat against the bisque.

The pate should pop off when you’re half to three quarters around.  Do not pry it off or use force.  Work slowly and gently.

Set the pate in a safe place to dry before packing it. It can easily be reset on the head with a small amount of plaster of Paris mixed in a baggie.  Snip one corner of the bag and apply the plaster as if you were decorating a cake. Press the pate in place and let set up for a few hours before handling
the doll.