Phil Weston maintained his fine start to the summer on a rain-interrupted day at Chelmsford, where Gloucestershire scored 296 for 6 from 86 overs.
The left-hander passed 50 for the fourth time in six innings in the Second Division of this year's County Championship, but he will have been bitterly disappointed at his dismissal.
Weston had reached 62, in an innings including seven boundaries, when he was tempted into a pull from a short Ryan ten Doeschate delivery.
But he only succeeded in offering up a simple catch to Ravinder Bopara at square leg to gift Essex their first bowling point.
Chris Taylor also scored a half-century before he drove over the top of a delivery from left-arm spinner Tim Phillips and was bowled for 66, containing 10 fours, while Ian Harvey goes into the second day in sight of a century. He reached the close on 72 and produced the most entertaining batting of the day.
The South Australian opener Mark Cosgrove provided the batting fireworks for Glamorgan as Worcestershire legend Graeme Hick celebrated his 40th birthday at New Road.
Cosgrove, 22 next month and born in the year that Hick made his county debut, plundered 61 from 91 balls in Glamorgan's first-day total of 133 for 3.
The stocky left-hander played his attacking shots with raw power, driving Nadeem Malik over long off for six and hitting 11 fours.
Hick quietly stood in the slips for 25 minutes in the morning and for two and a half hours after tea as frequent showers permitted only 44 overs of play.