What phrase best describes a blank expression?

Here are a few phrases that best describe a blank expression, depending on the specific nuance you want to convey:

Neutral:

* Blank stare

* Vacant look

* Expressionless

* Impassive

* Unreadable

Negative:

* Deadpan

* Emotionless

* Hollow

* Blank canvas (Figurative)

* Zombie-like

Positive:

* Serene

* Tranquil

* Peaceful (Though these may be more appropriate for a relaxed expression, not necessarily blank)

The best phrase will depend on the context and the specific effect you are trying to achieve.