The phrase "firm expression" is correct and can be used in written English.
It is used to describe someone's facial expression that conveys determination, confidence, or strictness. Example: Despite her petite stature, the principal had a firm expression that demanded respect from the students.
He had such a firm expression on his face that she began to give some credence to what he'd said.
Victoria Sharp London Music Masters Jeremy Hunt's firm expression of commitment to the arts on all levels, from local to national, is enormously encouraging.
With Romney, Huntsman and Santorum it is also a firm expression of their religious convictions, as all are devout Mormons or Roman Catholics whose faiths put an emphasis on having large families.
His tight lips and posture add to an overall firm expression.
As yet, there has been no firm expression of interest in him from Real Madrid, with Arsenal having made the only firm move, although Chelsea have also been touted as considering a bid for Suarez.
There's always a lot of uncertainty and provisional statements, which are heavily qualified, can be seized upon as firm expressions of policy.
Friendly is assisted, of course, by the subject matter of his documentaries, which frequently involve issues that invite firm expressions of opinion.
Philip Marshall QC, acting for the club on company law issues, said the board had narrowed down a field of 130 inquiries – from which 27 firm expressions of interest had arisen – with the advice of Barclays Capital and had accepted the best offer.
There's always a lot of uncertainty — and provisional statements, which are heavily qualified, can be seized upon as firm expressions of policy.
Use friendly but firm expressions, like, "I'm not happy about______.
His round, pink-checked face assumed the firm, benevolent expression of a man who is about to remove a painful splinter from a child's finger.
