Two newspaper advertisement placed in a London newspaper in this year reveal that Hawkins had opened a manufactory there to make and sell his upright patent pianofortes. The first of these reads:

HAWKINS' PATENT PIANO-FORTE/ distinguished from all others, by spiral strings and/ metallic frames. Their decided superiority for sweetness of tone and delicacy of touch is acknowledged by all amateurs/ and judges of music. The strings being stretched in a metal/ frame by screws, on a new plan, effectually prevents the In-/ strument going out of tune by the changes of the atmosphere;/ and their spiral form affords a fine mellow bass in a small/ compass. the increasing demand has induced the Patentee/ to open an Additional Warehouse, for the better acommoda-tion of the Public. No 33, Golden-square, where they may/ be supplied with every variety, as well as at No.4, Dalby/ Terrace, City Road.

The second gives more detail on the dimensions of his cabinet model.

PIANO-FORTES with SPIRAL SPRINGS / J I HAWKINS has now completed a few of these/
Instruments without valves, but the same in other respects/ as those which have already received the most unqualified ap/ probation of amateurs and professors of the first rank. No/ change of weather can ever put these Piano’s [sic] out of tune;/ and his Grand Pianos are in the form of a cabinet of only 44/ inches in height, 40 in breadth, and from twelve to 18 inches/ deep. – No. 4, Dalby Terrace, City Road, near the New/ River. (The Morning Post 3 June 1805)

According to his own testimony in an account given on the history of his development of the Claviole, he began to manufacture the first instrument made to this design in this year (Hawkins 1845, Mechanics Magazine, p124.)

Hawkins says he completed building his first Claviole in London this year (Hawkins, 1845 Mechanics Magazine, p 124)

Hawkins became bankrupt.  An advertisement in The Public Ledger on 1 June 1807  attempted to persuade readers that developing instruments made to his Claviole patent would make them a great deal of money as an inducement to purchase the patent rights, both English and American.

TO THE MUSICAL WORLD – An Opportunity of realising immense Wealth.

THE CLAVIOLE. – The Amateurs of Music/ have not an opportunity of viewing the grand desiderat-/ tum of the Musical World, for the past ages. The above Instru-/ ment, invented by Mr John Isaac Hawkins, and which has been/  twelve years  occupying the chief of his time at an immense ex-/ pence, is now finished, and a Patent is secured. This instrument/ being played by a Piano-forte, the performer gives the power of/ a full Band, combining the force and expression of the Violin/ with the sweetness of the Musical Glasses, and grandeur of the/ Organ. It is a keyed Instrument, with gut strings, and is made/ in form of a book-case, or chamber organ; it imitates wind as/ well as stringed instruments.

As the ingenious but unfortunate Inventor is a Bankrupt, the/ Patent, which includes sundry valuable improvements on the/ Piano-forte, and other Musical Instruments, will be SOLD by/ AUCTION, by Order of the Assignees, at the Patentee’s house,/ No. 4, DALBY TERRACE, City-road, near the New River/ on TUESDAY, THE 16TH June.

At the same time will be sold Twelve of the Patentees elegant patent Grand and Square Piano-fortes, with spiral strings, and me-/tallic frames. Also, the only Claviole ever finished. The Sale/ will begin at Eleven o’clock. This first Lot will be the English/Patent, and the second lot an American Patent for the same./ Either of these Inventions, in the hands of an active person, with  adequate mens to give them publicity, must prove an inexhausti-/ ble source of wealth. The advantage of a monopoly of an In-/strument possessing the powers of the Claviole, and which cannot/ go out of tune, must be obvious to every one.  The Piano fortes/ are peculiarly adapted for the export trade to the East or West/ Indies, the moisture or dryness of the atmosphere having no ef-/fect upon them. They have lately received the most marked/ approbation of persons of the first rank, and convincing proofs/ will be communicated at the time of sale of their superiority over/ all others.

They will be on view at Mr. Hawkin’s house, Dalby Terrace, on 8th, 10th, 12th and 15th June instant, from Twelve till/ Four o’clock. The Patentee will attend to give all requisite ex-/ planations... (The Public Ledger, 4 June 1807)

[Author's note: There is resonance here with the development of Plenius' Lyrichord during the 1740s, he having been persuaded by his backer, Charles Cope's assertions that it would make them both very rich if fully developed. (see: Margaret Debenham and Michael Cole, 2013: ‘Pioneer Piano Makers in London, 1737–1774: newly discovered documentary sources’in The Royal Musical Association Research Chronicle Vol. 44 Issue 1, Abingdon: Routledge, Taylor and Francis Group, 55-86)

An announcement placed in The London Gazette on 11 July 1807 states that John Isaac Hawkins would be granted his Certificate of Bankruptcy unless due cause is shown to the contrary by 2 August 1807.

On 1 June of this year a short news item in The Scots Magazine announced that:

Mr J.I. Hawkins, of Titchfield-/ street, has established a museum for/ the reception and exhibition of useful/ mechanical inventions and improve-/ ments. Although his own inventions/ constitute the leading feature of the/ exhibition, yet it is not exclusively/ confined to these, for the inventions/ and improvements of other are and/ will be introduced. In the list which/ he gives of those that are now exhi/ biting, or in preparation, may be no-/ ticed the following curious contrivan-/ ces: a cock, by which a servant can/ draw no more liquor than is ordered;/ - a machine, to be towed across a river, which will in the same moment/ draw on paper, to any reduced scale,/ the exact shape of the bottom; shew-/ ing at one view, the depth of water/ in every part, together with the width of the river; - a violin to fold up for/ the pocket; - artificial ears to assist the deaf, which can be worn out of sight/ without inconvenience. (The Scots Magazine, 1 June 1808. p445)

[Author’s note: newly identified information, sourced by Debenham, 19 August 2017]

An auction notice placed by William Abbott and Mr Blades in London includes 'a patent Claviole by Hawkins' (The Morning Post, 20 June 1808)

On 29 April 1809, a notice placed in The London Gazette announced that the Commisioners in a Commision of Bankrupt in the case of John Isaac Hawkins would meet to make a Dividend of his Estate and Effects on 3 June 1809.

An advertisement placed in The Morning Advertiser, 2 June 1809 for an auction sale to be held on 7 June by R Needham of Broad-street, Royal Exchange includes:

a valuable Assortment/ of curious and useful Musical Instuments and inventions/ from Hawkins's Museum, No 79, Great Titchfield-street,/ sold to ascertain damages against a Merchant, for not ful-/ filling his contract'. It also states 'The whole may be viewed on Mon-/day and Tuesday, and morning of sale, when a Gentleman/ will attend to perform on the claviole, from eleven to three/ o'clock.

On 2 November 1809, Hawkins took out a Patent for ' a certain Instrument, Machine or Manufacture, applicable in Mechanics as a Balance or Equipoise' (The Repertory of Arts, Manufactures and Agriculture  Vol XVIII – Second Series, 1811, P199-203)

According to his own account in The Mechanics Magazine, 1845 p.126, on 22 June 1812 Hawkins published a prospectus for a proposed 'Millechord Claviole, or thousand stringed Viol.', extract as follows:

...to be constructed with one thousand gut strings, the tones produced by rosined horsehair bows, and artificial fingers, acted on by four sets of finger keys and eighty pedals, together with barrels of large dimensions, which, with the bows, will be turned into machinery, giving the full power and variety of a band of two hundred performers.

The instrument will yield the perfect sounds of the violin, viola, violincello, double bass, harp and organ; will closely imitate the flute, clarionet, oboe, bassoon, fife, flageolet, union pipes, horn, trumpet, bugle horn, musical glasses, celestina, eolian harp &., as well as produce sounds entirely new and peculiarly delightful; and will scarcely ever be out of tune.

The prospectus goes on to say that the estimated cost would be £4,200 which he proposed to raise by subscription shares with a projected completion of the following spring - and suggested that there would be a huge profit for the shareholders on their investment.

[Author's note: Clearly this was a wildly ambitious and unrealistic proposition. It demonstrates too that Hawkins must have failed to sell the patent rights in the 1807 auction sale.]

The text of the prospectus also states that he had made a claviole with sixty-six gut strings and one set of finger keys in Philadelphia ten years earlier; a second in London, six years earlier and a third two years earlier.

Writing in 1845, he observes that because of pressure of work on other engineering projects, he did not have time to promote this prospectus and so nothing more was done with it at that time (that is to say in 1812).