The phrase (as) bold as brass means confident to the point of impudence.
The earliest recorded instance of the phrase is from the slang glossary in Life’s Painter of Variegated Characters in Public and Private Life (London, 1789), by George Parker (1732-1800), soldier, actor and public lecturer, self-appointed “Librarian to the College of Wit, Mirth, and Humour”:
He died damn’d hard and as bold as brass. An expression commonly used among the vulgar after returning from an execution.
The earliest occurrence that I have found is from the poetry section of The Hampshire Chronicle; and Portsmouth and Chichester Journal (Winchester, Hampshire) of Saturday 23rd June 1798:
On the Defeat of the French at St. Marçou.
WHEN Muskein, Gallic Chief, with bullets heated,
Attack’d in vain Marçou, he soon retreated;
As bold at brass he came, but prov’d a rogue,
So slunk dismay’d, and beaten to La Hogue.
Once thro’ a casement a felonious Scot
His head and shoulders had securely got;
But being check’d, and question’d in this strain,
“Where art thou going, Thief?” cry’d ‘Bauk again!’
Aided by the alliteration in b (bold – brass), the phrase (as) bold as brass arose from a long-established figurative use of the noun brass, sometimes in association with the adjective bold.
For many centuries, brass has been taken as a type of hardness, imperishableness, insensibility, etc.; for example, the Book of Job, 6:12, is as follows in the Later Version (1395) of the Wycliffe Bible:
Nethir my strengthe is the strengthe of stoonus, nether my fleisch is of bras.
In the King James Version (1611), this verse is:
Is my strength the strength of stones? or is my flesh of brasse?
In Thee first foure bookes of Virgil his Æneis (Leiden, Holland – 1582), the translation of the Aeneid, by the Roman poet Virgil (Publius Vergilius Maro – 70-19 BC), the Irish literary scholar and translator Richard Stanyhurst (1547-1618) combined bold and brass to form the adjective brass-bold; he used the sentence “a brasse bold merchaunt in causes dangerus hardye”, in which:
– merchant means a person skilled (in a particular activity);
– hardy means audacious;
– bold means stout-hearted;
– brass denotes hardness and strengthens the meaning of bold.
The context in which that sentence occurs is as follows: The Greeks have feigned retreat and left outside Troy a hollow wooden horse in which Greeks soldiers have concealed themselves; Sinon, a Greek warrior, surrenders himself to the Trojans in order to trick them into bringing the horse into their city.
Stanyhurst writes that, with loud shouts, Trojan shepherds bring to Priam a youth whose hands are tied behind his back; this guest slyly offered himself for captive in order to contrive to open Troy to his Greek fellowmen; he stands ready for either engaging in deception or finding certain death:
With shouting clamorus hallow
Of Troy towne the shepheerds a yoncker mannacled haling
Present too Priamus: this guest ful slylye dyd offer
Hym self for captiue, thearby too coompas his heasting,
And Troian citty to his Greekish countrye men open.
A brasse bold merchaunt in causes dangerus hardye.
In doubtful matters thus stands hee flattlye resolued,
Or to cog: or certeyn for knauerye to purchas a Tyburne.
If challenged to a private dispute, his impudence bears him out. He counts it the onely errour to confesse he hath erred. His face is of brasse, which may be said either ever or never to blush.
In the first lines of the Prologue to No One’s Enemy but His Own (Dublin, 1764), the Irish author Arthur Murphy (1727-1805) used bold and brass in close proximity to characterise the dramatist’s audacity in having his play staged and therefore lambasted by critics as well as complained about by the actors themselves:
Bold was the man, and fenc’d in ev’ry part,
With oak, and ten-fold brass about the heart,
To build a play who tortur’d first his brain,
And then dar’d launch it on this stormy main [= open ocean].
It is popularly—but erroneously—claimed that the phrase (as) bold as brass originally referred to Brass Crosby (1725-93), Lord Mayor of London.
For example, according to this website, Brass released in 1770 a newspaper editor who had illegally published the day’s business in Parliament. As Brass had gone against the wishes of Parliament, he was thrown in the Tower of London, but, when he was brought to trial, several judges refused to hear the case and, after protests from the public, he was released.
For that reason, says that ludicrous theory, bold as Brass became a common saying…