A fifth wicket stand of 254 from Ben Kellaway and Colin Ingram put Glamorgan in a strong position by the end of day 3 as they led Gloucestershire by 148 runs on first innings, before the West Country county closed on 12 without loss.
Resuming overnight on 52 and 55 respectively, the pair started the day strongly with both completing centuries in the first session (Ingram reaching 100 is here on you tube), before later falling for 117 (Ingram) and 137 (Kellaway).
An excellent 75 from Chris Cooke with support from the lower order helped Glamorgan to an imposing total of 528.
Scorecard and report from cricinfo