The Slacks came from Common Side, where Isaac was living in 1841 (aged about 20).  The family was involved in making spring cutlery.  By 1849, Isaac was listed as a spring knife manufacturer at Springhill, Crookes.  Henry Thomas Grinold was also a spring knife cutler, who in 1841 was living in Green Square, Charles Lane.  He had been born in Attercliffe.  In 1852, he was listed as a spring-knife manufacturer in Fitzwilliam Street (and living in a courtyard in Broomhall Street).  He was briefly in partnership with Stacey Bros until 1854.  By 1856, Grinold had moved to a working address in Eyre Street, with a residence in Clarence Street.  Isaac Slack was listed in that year as a clerk in Spring bank.  In 1860, Slack & Grinold advertised at Bath Works, Bath Street, as a manufacturer of a wide range of ‘Celebrated Cutlery’, especially pen, pocket, sportsman’s, pruning, lock, and spoon knives.  The advertisement stated that ‘None are Genuine Unless Stamped’ with the corporate mark: a picture of two diamonds and an oblong shield.  By 1865 (when it advertised again), the company had adopted the simpler ‘ONWARD’ mark, which had belonged to John Sayles at Bath Works.  The partners were Henry T. Grinold, living in Cemetery Road, and Isaac Slack, in Palestine Place, Broomhill.  Slack died on 8 September 1877, though the name was retained.

In the 1880s, Slack & Grinold traded from Bath Works, Sylvester Gardens.  Its last address was Bath Works, Napier Street.  In 1900, Grinold retired and disposed of the business to his nephew John Sayles.  Within a year or so, the marks were sold to Michael Hunter.  Henry Thomas Grinold died, aged 85, on 19 December 1906 and was buried in Ecclesall Cemetery.  He left £2,868.  Needham, Veall & Tyzack later owned the ‘ONWARD’ and ‘BON ACCORD’ marks.