In Australian English, the colloquial name Jack the Painter denoted a coarse green tea drunk in the bush.

According to Gerald Alfred Wilkes (1927-2020) in A Dictionary of Australian Colloquialisms (Sydney University Press in association with Oxford University Press Australia, 1990), this name referred to the fact that this tea was “apt to colour the utensil or the mouth”.

But, according to John Barr in The Shanty on the Rise…., published in the World’s News (Sydney, New South Wales, Australia) of Saturday 11^th November 1939, the name Jack the Painter referred to the colour of this tea and to its awful taste—this explanation is supported by the texts containing the very first occurrences of the name, which all mentioned the flavour of this tea. This is John Barr’s text:

Tea Much Cheaper

To the mutterings of Brigid Hogan, missus of The Shanty, against the abrupt rise in tea, the commercial turned a conciliatory smile.
“It is a mere matter of relativity, ma’am,” he remonstrated. “There have been early emergencies in Australia when the price of tea was as high as Gilderoy’s kite.
“At one time most of our tea came from China, and housewives had to pay up to £16 16s per chest of 50.b., over 6s a lb. Buying it retail made the cost much more. That was known as Hyson-skin, H.S., or Congow tea. There were cheaper, and very bad, teas, known to consumers as ‘post and rail,’ because of the number of sticks and long leaves in it, and ‘Jack the Painter,’ because of its green tinge and gawdawful taste when brewed.”

Note: The male forename Jack, originally a pet form of John, has been applied in a wide range of general and specific contexts.
—Cf., for example, the phrase before one can say Jack Robinson, and similar uses of Johnny in Johnny Foreigner and Joe in Joe Soap.

The earliest occurrences of the name Jack the Painter that I have found are as follows, in chronological order:

1-: From The Port Phillip Patriot and Morning Advertiser (Melbourne, Victoria, Australia) of Wednesday 20^th May 1846:

“Jack the Painter.”—There are few of the mercantile community, in this or the neighbouring colonies, but who are perfectly cognizant of the cognomen of “Jack the Painter,” as bestowed upon a shipment of tea which reached us some years ago, the flavor of which not being in accordance with general taste is the special horror of all shepherds and hutkeepers. Not having heard anything of the “gentleman” for some time past, we were in hopes that Time the great destroyer of all things, had in its progress demolished the well known shipment per Orwell. On Monday, however, the subject was again revived by a servant describing amongst other nourishing rations which had been served out to her, the well known “Jack the Painter.” The magistrates smiled as if perfectly cognizant of the flavour of the delicious beverage, and readily credited her assertion, that her place did not suit her to a “tea.”

2-: From A Tale, an unsigned story published in The Geelong Advertiser, and Squatters’ Advocate (Geelong, Victoria, Australia) of Friday 19^th February 1847:

In a slab hut, seated by a table of the same material, cheered, after a dreadful drenching, by the warmth of a pile of blazing she-oak logs, and luxuriating, after a fast of some fourteen hours, on a plentiful supply of mutton, damper, and tea (the latter, by the way, being of that peculiar flavor termed ‘Jack the painter,’ alias ‘post and rail,’ for which, however, many apologies were offered, and the cupidity of a certain storekeeper sadly growled at); […] under such circumstances, succeeding a ‘wild goose chase’ after a mob of stray cattle, in which he had reason to suppose were some of his own brand, was placed, on the 31^st day of October, 184–, your humble servant.

3-: From A Peep at Maneroo, Eden, and Boyd, published in Bell’s Life in Sydney and Sporting Reviewer (Sydney, New South Wales, Australia) of Saturday 4^th March 1848:

We were greeted by the solitary resident on the establishment, who, in his own person combined the respective avocations of Super! Overseer! Storekeeper! Butcher! Baker! Cook! and Assistant Blacksmith! We surprised him in the act of ablution, having just put down a Johnny Cake in the smouldering embers, while a poley-quart-pot simmering at the fire, indicated that it was ready to receive the “pinch of Jack the Painter.” […] Before leaving, we cast a curious eye over the once well-filled shelves and compartments of the store, but the stock-in-trade had dwindled almost into a nutshell, and was easily embraced at a glance, comprising as it did only the following articles:—five bonnets, trimmed a la Jenny Lind, for the female cannibals daily expected from Church-hill; two pieces of moth-eaten petticoat dimity for ditto; one dozen hooks and eyes, one paper mixed needles, a skein of twine, one hank of whitey-brown thread, half a chest of “Jack the Painter” tea, half a chest postern rails tea, two dozen infant’s Highland socks, (these, by the way, are ordered to be reserved for the Big Squatter’s special appropriation when he visits the district); one mouse-trap, three hurdle nails, and a broken gimlet. A few empty sugar-bags were scattered about the yard, on which no fewer than seven cats, with their families, were basking in the sun.

4-: From Our Antipodes: Or, Residence and Rambles in the Australasian Colonies. With a Glimpse of the Gold Fields (London: Richard Bentley, 1852), by the British-Army officer Godfrey Charles Mundy (1804-1860):

At one of these fords an old settler, living on a bit of cleared land near it, stopped our progress by his well-timed advice to wait awhile for the partial subsidence of the flood, which the tide-mark proved to be sinking. He brought us some black damper and a dry chip of cheese, (for we were famished,) together with a hot beverage in a tin pot which richly deserved the epithet of “post and rail” tea; it might well have been a decoction of “split stuff” or “iron bark shingles,” for any resemblance it bore to the Chinese plant. Another notorious ration tea of the bush is called “Jack the painter.” This is a very green tea indeed, its viridity evidently produced by a discreet use of the copper drying pans in its manufacture.

5-: From The Geelong Advertiser and Intelligencer (Geelong, Victoria, Australia) of Thursday 27^th January 1853:

PUBLIC HOUSES AT THE DIGGINGS.

There is an intense selfishness and a most pitiful display of opposition to the Government, evinced by the representatives of the people in the votes recorded against the extension of Public Houses to the Diggings. Morality is made a cloak of to hide a wrong inflicted on nearly a moiety of the population of the colony of Victoria. […] A legislator may be refreshed by brandy, hollands, port, sherry, moselle, sillery, and nobbIers “ad nauseam,” but a digger not being compounded of such transparent porcelain must be content with “Jack the painter” and a pannikin of dirty water, to cool him down to a moral point, and conserve his principles in accordance with Mawwormism *.

* From the name of a character in The Hypocrite (1768), by the Irish playwright Isaac Bickerstaffe (c. 1735–c. 1812), the noun Mawworm designates a hypocritical pretender to sanctity.

6-: From Combinations, published in the People’s Advocate and New South Wales Vindicator (Sydney, New South Wales, Australia) of Saturday 25^th June 1853:

It will be in the remembrance of our readers, that tea of an infinitely superior quality to that now in general use could have been purchased in abundance for little more than prime cost at the night Auctions, which the shopkeepers, and “big auctioneers,” contrived to suppress, because their dealings interfered too closely with their monopoly. At the present moment there are scarcely any teas retailed but those of inferior descriptions; and it is notorious that our colonial importers of this commodity, never send for the finer sorts which are all bought for Europe. The worst sorts are reserved in Canton, for New South Wales, for which “Jack the Painter; and “Posts and Rails,” are considered eminently adapted.