Richardson took his second-innings tally to four wickets by claiming one this morning, making it 12 for the match for the second outing in a row after claiming a dozen in the victory over Kent.
The home side had the visitors staring at defeat on 160 for seven at lunch, trailing by 63 runs in their attempt to avoid an innings defeat in a rain-hit match.
Gloucestershire were indebted to eighth-wicket pair Gareth Roderick and James Fuller, who were both unbeaten on 27 and had put on a stand of 53.
Darren Stevens completed his century as Kent took a first-innings lead of 84 runs against Essex at Chelmsford.
Stevens went on to score 136 out of Kent's 296 in reply to Essex's 212 on the final day of a match heading for a draw. By lunch, Essex were 18 without loss to trail by 66.
Liam Dawson hit an unbeaten half-century as Hampshire made inroads into the first-innings 295 of Lancashire at Southampton.
Dawson reached lunch on day three on 55 not out and with the 43 contributed by Michael Carberry the home side were 107 for two at the break, trailing by 188 runs.
Scott Borthwick scored his second half-century of the match as Durham pressed home the advantage in their Division One clash with Middlesex at the Riverside.
Borthwick was unbeaten on 55, to add to his earlier 52, from a total of 177 for four to give his side a lead of 240.
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