From 1615 Sir Robert had been interested in the manufacture of glass, a share in the monopoly of which he had secured in that year. There is a brief reference to this matter of glass-manufacture in the D.N.B., but much fuller detail is given by C. A. Maunsell and E. P. Statham in History of the Family of Maunsell (Mansell, Mansel), i, chap. xii. From a statement made by Sir Robert in defence of his patent during the debate in the Commons on the Monopoly Bill in 1624 it would appear that he endeavoured to establish factories in various places — London, the Isle of Purbeck, Milford Haven, and the Trent Valley. John Brand (Hist. of Newcastle) says — ‘We may venture to fix the beginning of the glass-works upon the Tyne about 1619, where they were established by Sir Robert Mansell. … The cheapness of sea-coal was no doubt his chief inducement for erecting them at so great a distance from London.’

The reference to sea-coal is significant. As Sir Robert's process involved the use of sea-coal instead of wood the monopoly was to some extent of the nature of a legitimate patent, but it was constantly necessary for him to defend it against those who wished to infringe the patent and against those who attacked monopolies; for details see Maunsell and Statham, op. cit., where also is reproduced the title (in facsimile) and the text of A True Report of the Service done vpon Certaine Gallies passing through the Narrow Seas; Written to the Lord high Admirall of England, by Sir Robert Mansel Knight, Admirall of her Maiesties forces in that place (London, 1602).

Sir Robert, who d. in 1656 (his will was administered by his widow on 20 June 1656), had been twice m.: (1), before 1600, to Elizabeth, daughter of Sir Nicholas Bacon, lord keeper, and (2), 1617, to Anne, daughter of Sir John Roper. There was no issue of either marriage.

From 1615 Sir Robert had been interested in the manufacture of glass, a share in the monopoly of which he had secured in that year. There is a brief reference to this matter of glass-manufacture in the D.N.B., but much fuller detail is given by C. A. Maunsell and E. P. Statham in History of the Family of Maunsell (Mansell, Mansel), i, chap. xii. From a statement made by Sir Robert in defence of his patent during the debate in the Commons on the Monopoly Bill in 1624 it would appear that he endeavoured to establish factories in various places — London, the Isle of Purbeck, Milford Haven, and the Trent Valley. John Brand (Hist. of Newcastle) says — ‘We may venture to fix the beginning of the glass-works upon the Tyne about 1619, where they were established by Sir Robert Mansell. … The cheapness of sea-coal was no doubt his chief inducement for erecting them at so great a distance from London.’

The reference to sea-coal is significant. As Sir Robert's process involved the use of sea-coal instead of wood the monopoly was to some extent of the nature of a legitimate patent, but it was constantly necessary for him to defend it against those who wished to infringe the patent and against those who attacked monopolies; for details see Maunsell and Statham, op. cit., where also is reproduced the title (in facsimile) and the text of A True Report of the Service done vpon Certaine Gallies passing through the Narrow Seas; Written to the Lord high Admirall of England, by Sir Robert Mansel Knight, Admirall of her Maiesties forces in that place (London, 1602).

Sir Robert, who d. in 1656 (his will was administered by his widow on 20 June 1656), had been twice m.: (1), before 1600, to Elizabeth, daughter of Sir Nicholas Bacon, lord keeper, and (2), 1617, to Anne, daughter of Sir John Roper. There was no issue of either marriage.