The original Jameson Cell design had the following features:
* small (200 mm diameter) downcomers
* no wash water
* no tailings recycle
* no bubble dispersers
* low capacity.
In 1994 MIM launched the Mark II model Cell. It incorporated the following changes:
* the downcomer diameter was increased to 280 mm
* wash-water trays were included for froth washing
* a tailings recycle system was added to maintain constant downcomer flow and higher recoveries
* conical bubble dispersers were added
* increased depth of tank from the bottom of the downcomer
* increased distance between the downcomers. 
These changes resulted in a higher capacity design.
One of the problems encountered with the Mark I Cell was that its performance was reduced if the feed rate to the cell varied, which was a common occurrence arising from normal fluctuations in operating concentrators. This problem was resolved by recycling some of the tailings to the cell feed via an external splitter box called an "External Recycle Mechanism" or "ERM" box separate to the flotation cell. Thus, when the production of the feed stream to the Jameson Cell decreased as a result of a fluctuation elsewhere in the concentrator, a higher percentage of the tailings was automatically recycled to the downcomers, producing a constant flow rate, hence feed pressure, to the cell. This had the added benefit of giving a proportion of the tailings (typically 40%) a second pass through the system, which resulted in higher recoveries. In coal fines flotation, this allowed a single Cell to achieve the same recovery of combustibles as had previously been achieved in some two-stage Cell systems. 
Subsequently, an internal recycling system, referred to as the "internal recycle control" or "IRC" was developed. This was mainly used in integrated rectangular cells (see Figure 6), where the feed tank and tailings recycling system could easily be built in a single unit with the flotation cell. This system reduced the cell installation costs and made the cell more compact.
During this period, the orifice diameter was increased from the 28 mm design used in 1990 to 34 mm with the Mark II model and 38 mm in 1997. This, together with the larger Mark II downcomer diameter, allowed the slurry flow per downcomer to be doubled from 30 m/h in 1990 to 60 m/h in 1997.
The increased distance between the downcomers reduced the interaction of aerated slurry discharging from adjacent downcomers. This interaction could reduce overall cell recovery by causing particles collected by bubbles in the downcomer to detach in the pulp tank.
There was significant turbulence in the areas beneath the downcomers. that could result in particles detaching from bubbles. These turbulent areas were calmed by the addition of conical diffusers beneath each downcomer. They allowed uniform bubble rise velocities across the surface of the cell by slowing the superficial gas velocity in the high void-fraction area immediately around the downcomer and provided a more even bubble dispersion. It was reported that the diffusers reduced the turbulence by 69% compared with a standard downcomer with no diffuser.