Thomas was an Engineer/ Wheelwright. It is possible that Thomas was married some time before he married Lydia Barnes and that he had three children by his first wife.
These children were as follows.

George was born c 1817 in Surrey or Greenwich.
Charles was born c 1820.
Mary Ann was born c 1826.

Thomas came from Windsor Forest, Berkshire, U.K. He was a skilled Mechanical Engineer and was working for Thomas Kent in London. Mr. Kent was planning to bring his family and several servants to Australia along with a steam engine built by his firm in London. Passage had been booked on the "Harmony" but it was felt that the engine would be too heavy for the boat with the number of passengers.
Thomas Blay was convinced to emigrate to Australia by Mr. Kent and a Mr. Levey who promised him employment at very liberal wages as well as other flattering inducements. Thomas brought his wife and four children to Australia on the ship "Harmony" in 1829. It left London on 13 September, 1828 and arrived in Port Jackson on 14 March, 1829.
The Blays had Charles, Mary Ann, and Henry with them when they departed. Their second son was born during the trip and was named Harmony in honour of the boat. Thomas was listed as an English settler and the family travelled steerage. They had with them 2 Chests, I Box, 2 Trunks and 2 Beds. The contents were listed 3,,; wearing apparel and tools. The family name was listed as Blay. AO Reel 1263.
Once here Thomas found his circumstances were not as promised. III 1830 he applied for a land grant to commence his own manufactory for steam and other engines. He also wanted a small grant of land for cultivation for the employment of his wife and children. Reel No. 1096. A list of machinery that Thomas intended to make at his manufactory accompanied his request as well as a list of items already made by him in the, Colony. These included axles, a machine for making combs, the first screw cutting machine ever made in the Colony and a slide safe valve for the vapor bath at Government House. Unfortunately no land was available.
Thomas and Lydia were living in a dwelling house in Pitt Street, Sydney at the time of Henry's christening and they remained there for several years. Thomas was working as a Blacksmith in 1836 according to the Electoral Roll for that year.
Thomas and Lydia had six children.
There was some financial trouble for Thomas in 1838. A summons was issued by Brent Clement Rodd, a lawyer, in the Supreme Court 17 September, returnable 25 September for payment of 50 pounds on promises. The court found in favour of Mr, Rodd and damages were awarded on 11 October, 1838 in the amount of eleven pounds, one shilling and five pence. A notice appeared in the Government Gazette dated 13 October, 1838 stating that "In the Supreme Court - Rodd v. Blay - On the defendant's premise in Pitt Street, on Saturday next, the 20th day of October instant, (unless this execution be previously satisfied) the Sheriff will cause to be sold all the Right, Title and Interest of the Defendant, of, in, and to - A Lot of Iron and 2 pair Smith's Bellows as well as Household Furniture."
According to the Assessment Books for 1845, Thomas was living al: 143 Pitt Street, in a rented house owned by Ellen Sewell. The house was a single level, two-roomed cottage with a shingle roof.
Thomas died of decline of years aged 66. He was buried at 4 pm at Camperdown, Section 5, Butt No. 971. There is no headstone.

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To His Excellency, Lieutenant General Ralph Darling, Governor and Commander in Chief in and over the Territory of New South Wales and its Dependencies, Vice
Admiral of the same etc. etc.

The Respectful Petition of Thomas Blay late of Windsor Forest, Berkshire, Artizan.

She with,
That Petitioner is a sound, practical Mechanic, and arrived in this Colony about twelve months ago on the Ship Harmony (Capt. Irelands) bringing with him his wife and five children.

That Petitioner has been induced to emigrate under the auspices of Mr. Levey and a Mr. Kent, by whom he has been grossly deceived, in as much as they promised to employ Petitioner at extremely liberal wages, and offered other flattering inducements to Petitioner to emigrate; but that so far from those promises having been fulfilled Mr. Kent has recently made a demand upon Petitioner for the expenses of his passage from England.

That Petitioner finding himself so circumstanced, and not despairing but that he should meet with encouragement at the hands of your Excellency, has spent much time in personal observations, and has likewise been -industrious in his enquiries of men of judgement, in order to come to a satisfactory and conclusive opinion, how far, in the event of establishing a Manufactory, his ingenuity, acquirements, and labour might produce success, the pursuit of which has induced Petitioner to appeal to your Excellency.

That Petitioner is desirous of erecting an Establishment for the manufacture of Steam and other Engines and Machinery in general, which must be of infinite utility to the growing consequence and interest of this Colony.

That Petitioner has tools, and capable Mechanics in readiness of commence such Manufactory, and Friends in command to support him in the erection of suitable workshops and Buildings.

Petitioner therefore humbly prays your Excellency will be pleased to grant him a very few rods of ground opposite Mr. Terry Hughes Brewery near Carters Barracks for the above purpose.

Petitioner likewise having a Wife and a numerous and young family, would humbly beg your Excellency will be further pleased to bestow upon him a small Grant of land in the interior for the purpose of cultivation for the employment of his wife and children, and your Excellency's Petitioner as is duty bound will pray.

No. 10 Castlereagh Street
Sydney 17th March, 1830

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Castlereagh Street, Sydney
29th March, 1830

Sirs,

According to your advice I proceeded to W. Cooper and stated to him what was expected by His Excellency the Governor to be done previous to my receiving any favours from His Excellency as prayed for in my Memorial. Mr Cooper without the least hesitation offered to write to His Excellency respecting the means of preceding with a general Manufactory and also to give his opinion as to the necessity of such an Establishment. I the following day saw Mr Kent who told me he had written to His Excellency upon the business and that I need not ask Mr Coopers .... else further questions concerning the matter from which I am led to believe Mr Kent has answered for Mr Cooper as well as himself such explanation as His Excellency the Governor required as to the means I can command for carrying on an Establishment of the magnitude proposed.
From the orders I have received for articles of mechanical process without solicitation; fully justifies me in presuming that Mr Cooper will act up to his professions in supporting me to execute any orders I may be favoured with let them be never so extensive.
Being unwilling to trespass too far upon your true patience, I humbly beg if it meets with your approbation that you will be pleased to lay before His Excellency the enclosed list of articles which I have not the least doubt I can Manufacture here under His Excellency's patronage, with to myself and with extensive benefit to the Colony.

.......... be most ready to afford His Excellency any further explanation that
may be required of me and sincerely trust I shall / through His Excellency's well known disposition to promote the interest of the Colonists in the object of my Petition.

I have the honour to be,
Sir,
Your most obedient servant,

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List of Machinery proposed to be manufactured in Sydney
by Thomas Blay

Steam Engines conducting high pressure and Locomotive
Hydraulic Engines for raising water from any depth to any height
Hydraulic force pumps and water closets
Curvilian straight Barrel lifting pumps
Beer Machines
Extinguishing and Garden Engines
Brass Cocks for Brewers, Distillers etc.
Hydraulic presses for packing wool etc.
Screw presses of wood and iron
Patent axles of all sorts
Common axles for Carts, Waggons & Coaches
Mill and Engine work of all sorts
Cranes and Gibs to raise any weight
Turning lathes for Brass, Iron and Wood
Screw Tackle and Mechanical Tools of every description
Agricultural Machinery
Practical & Experimental Machinery
Patent Leadpipe from 1/2 inch to 2 1/2 inch diam.
Machinery for Manufacturing Ropes
Brass & Iron Foundry work
Patterns and Models made to Drawings

Thomas Blay has already manufactured in this Colony:

Patent axles
Curvilinear Pumps
Slide Safety Valve for Vapour bath at Govt. House
Screw Cutting Engine (never attempted before in the Colony)
Machine for Making Combs

1. George Charles BLAY b: 1817 in Greenwich, UK
2. Charles BLAY b: 1820
3. Mary Ann BLAY b: 1826 in UK
4. Harmony BLAY b: 03 SEP 1828 in At sea on board the "Harmony"
5. Margaret BLAY b: 17 OCT 1831 in Redfern, Sydney, NSW
6. Sarah BLAY b: 03 JUL 1834 in Sydney, NSW
7. Eliza BLAY b: 29 AUG 1839 in Pitt St, Sydney, NSW c: 11 FEB 1842 in St Lawrence Parish, Sydney, NSW
8. Henry BLAY b: 28 SEP 1826 in Maidstone, Kent, UK