In this article Caimin O'Brien and Jean Farrelly focus on the archaeological and documentary evidence for the glass industry in seventeenth-century Offaly.

At the beginning of the seventeenth century the method of manufacturing glass in northern Europe had not changed since the Middle Ages. However, by the end of the century the advances in the glass industry had made the earlier technology obsolete. The main evidence for the manufacture of glass in this period comes from medieval documentary sources because the survival rate of glass-furnaces is very poor. In England there is no surviving upstanding forest glass wood-fired furnace of the sixteenth-seventeenth-century period, and several which have been excavated only survived to a few courses high. The discovery of an extant furnace with barrel-vaulted roof in situ in the town land of Glasshouse near the village of Shinrone in County Offaly offers the archaeologist a rare opportunity to examine the technology of an often-forgotten glass industry.

Two locational factors were necessary for establishing a glass-furnace: firstly, close proximity to woodlands where there was an abundant supply of fuel and ash from the burning process; secondly, a convenient source of sand, e.g. an esker ridge. The furnaces themselves were simple rubble-stone structures consisting of a barrel-vaulted firing chamber with a central fire-trench. The fire was fed from either one or both sides of the chamber via a stoking tunnel. The crucibles were placed in pairs on top of the sieges, which were located on either side of the fire-trench. Work holes (glory holes) were built into the side of the vault to allow the glass-makers to remove impurities which rise to the surface of the molten glass and also to check when the glass was ready for working. An iron pole was inserted into the crucible via the work hole, if the molten glass was ready a thread of glass would hang from the rod.

The resulting glass was green because of potassium oxide specifically found in wood, and was known as forest glass. Dry wood, producing little smoke, was essential as there no chimney to allow smoke to escape in the furnace. Moreover, it has the additional benefit of reaching higher temperatures. The furnace itself was enclosed by a wooden building or glasshouse, some examples of which were known to have been roofed with wooden shingles or slate. The post-holes or ditches of these buildings have been identified in excavations of forest furnaces in England.

Until the mid-sixteenth century the glass industry in England and Ireland was virtually non-existent, glass being imported from France. As an example of how precious glass was at that time, it is recommended that "when Duke of Northumberland left Alnwick castle the steward was accustomed to take out the glazed windows and stow them away safely until the Duke's return". In 1567 a Huguenot, Jean Carre, obtained a permit from Queen Elizabeth I to establish a forest glass industry in the Sussex/Surrey region. The workforce was recruited from experienced glass-making families centered in the Lorraine region. Among those recruited were the Hennezells (Henseys) and the de Bigaults/Bigots (Bigos).

In 1586 Queen Elizabeth I granted Captain Woodhouse suit for a privilege to make glass in Ireland. His assistance to George Longe and Ralph Pillying in erecting and maintaining two houses for glass making'. This was followed by the granting of a monopoly in 1589. In October 1589, a petition from George Longe to Lord Burghley stated that 'he has spent his time wholly in the trade and has found stuffe meet and brought to perfection the making of glass in Ireland'. Longe had bought the patent for glass-making from Captain Woodhouse in that same year. There are also references to land being granted to Philip de Bigo in County Offaly during the Elizabethan period.

By the early seventeenth century English manufacturers had developed coal-fired furnaces based in towns which were beginning to replace the wood-fired furnaces. An Englishman, Admiral Sir Robert Mansell, held the monopoly on this new technology. Furthermore, owing to the enormous depletion of woodland a royal proclamation in 1615 banned the use of wood fuel in glasshouses in England. The increased competition of Mansell, who also ensured the strict enforcement of the 1615 ban, pushed the French families out of the glass-making industry. In order to ply their trade, some of these French families moved to other countries which were not prohibited from using wood, Ireland included.

In 1619 Mansell issued an arrest for Sir William Clavell and Abraham Bigo. This may have been as a result of Clavell and Bigo's joint venture to establish a glasshouse at Church Knowle in Dorset in 1618. Four years later, in 1623, Abraham Bigo appears in Birr, Co. Offaly, having leased land from Lawrence Parsons to construct a glasshouse in the townland of Clonbrone, near Birr. Under the conditions of this lease Bigo could not 'set up any glass house or glasswork on any other land, or buy wood of any other for his glasswork but only of me'. In the reign of Charles II (1660-85) a namesake and descendant of the earlier Philip Bigo was granted land in Ballyneshragh, Carrowmore, Feddane and Newtown in Lusmagh, Co. Offaly, and according to local tradition he established some glasshouses in these areas.

In 1638/9 the exportation and manufacture of glass in Ireland was prohibited, and in 1641 another bill prohibited the felling of trees as a fuel supply for glass-furnaces. As happened in England twenty years earlier, the combined effects of the legislation and technological advances heralded the end of the forest glass wood-fired furnaces.

The Henseys are mentioned in Ireland in the seventeenth century in Garrycastle and Banagher in the parish of Lusmagh; Kilorney, Ballyengowne, Galrus, Ballyshane in Rynagh parish; Bollinure, Ballinkellin in Shinrone parish and Clonlisk, Ballintoren, Adrowle, Kellogs in the parish of Kilcommon, Co. Offaly. On the current edition of Ordnance Survey map the latter three townlands surround the Glasshouse site, which suggests that the furnace was associated with the Hensey family. In 1670 one Ananias Hensey set up a glasshouse near the new town of Portarlington, which was founded in 1666. The Calendar of State Papers for November 1670 states that Hensey was 'failing in his art of making glass' despite the fact that he had 'practiced it in another place these twenty years past'. Perhaps Hensey was trying by trial and error to make the transition from the old wood-fired furnace to the more efficient new technology of the coal-fired furnace. The site of this glasshouse may have been located at the 'Glasshouse' marked on the Ordnance Survey map west of the town.

In England the majority of glasshouse sites have been identified by the field-name Glasshouse, and of those identified only the lower portions of the furnaces survive. Two townlands in County Offaly are called Glasshouse. The earliest reference to the townland name of Glasshouse at Shinrone was made in 1717, which suggests that the townland received its name in the seventeenth century. Townland, close to the village of Shinrone, was found, after field inspection, to contain the upstanding remains of a seventeenth-century glass furnace. This is a typical barrel-vaulted crude sandstone structure with a central fire-trench and opposing stoking tunnels. The entire internal surface of the vaulted furnace is covered in a layer of blue/green glass. There are two work holes on one side wall at the springing level of the arch, and evidence of two destroyed holes on the opposite wall. The siege platforms are in place but the end walls do not survive.

The plan and section of this furnace correspond well with a mid-sixteenth-century forest glass-furnace at Blunden's Wood, Surrey, England (see section), and a seventeenth-century example at Jamestown, Virgina, America, dated to 1608. A large fragment of another glass-furnace with similar glass-covered surface was recovered from a field wall, along with fragments of glass, in the townland of Glaster, near Lusmagh. This site is associated with Philip Bigo in the 1659 census. The furnace at Glasshouse, Shinrone, is likely to fall within the date range 1590 - 1640, based on parallels with the above-mentioned furnaces. After the 1640s the wood-fired -furnaces were replaced by the technologically advanced, town-based, coal-fired furnaces. From the Elizabethan period up to the 1659 census both the Bigo and Hensey families were known to be living and plying their trade throughout County Offaly.

Acknowledgements:
We would like to express our thanks to the following people who generously gave their time and assistance in the preparation of this article: Mary Boydell, Annette Camier, Hon. Sec. of the Huguenot Society of Ireland, David Crossley, Sheffield University and Noel McMahon, Shinrone.