China Dolls
"China" dolls are those porcelain dolls that have been glazed. A soft sheen will appear over the porcelain when under a light.
Bisque Dolls
Bisque dolls are those porcelain dolls that are left unglazed, so that the color of the skin appears more "natural." Bisque dolls are often very subtly rougher to the touch than china dolls.
Authenticity
The authenticity of china and bisque dolls can often be verified by a maker's stamp and lot number located somewhere on the doll. Certain dolls will even come with certificates of authenticity.
History
Doll makers in France, Germany and Denmark started to produce porcelain dolls in the early 1800s. It wasn't until the late 1800s that these types of dolls became widely affordable. German manufacturers began to mass-produce porcelain doll heads, arms and legs, significantly reducing the cost of the dolls. But because this style of production necessitated less artistic design, French dolls are considered to be of a higher quality and more elegant.
Fun Fact
Porcelain dolls only represented adult figures until the introduction of the French "Bebe" style in the mid-1800s.