He paused for a few seconds, and his face hardened slightly.

Something of the thought must have shown on his face, for the voice hardened slightly.

The thread of tendon hardened slightly and held its shape.

Gabriel's handsome face hardened slightly as she come to stand before them.

Her eyes hardened slightly and Paul sensed he was on thin ice.

His father's gaze hardened slightly, then he reached out to ruffle Gaius's hair once more.

Slightly hardening the steel may decrease its gumminess and make it easier to cut.

His features hardened slightly then, and he turned away.

Ian took a deep breath, his long, homely face hardening slightly.

The cube ceased some of its quivering and seemed to harden slightly, offering more support.