Abstract: Methods and apparatus for measuring viscosity and/or surface tension of a liquid are described in which droplets are formed at a needle or pipette containing a sample of the test liquid and a size-related characteristic of the droplets such as droplet size, volume, diameter, or weight of the test liquid are measured by means of by capturing an image of the droplets and obtaining the size-related characteristic from the captured image. Subsequently or previously, a volume of the same sample of the test liquid is drained from the needle or pipette under pump pressure or a hydrostatic pressure, and an elution time is measured. The method and apparatus allows or includes determining the viscosity from the elution time, and determining the surface tension from the viscosity and the size-related characteristic of the droplet such as droplet size, volume, diameter, or weight of the test liquid.

Abstract: A direct electrostatic printing device includes a printhead structure with apertures and control electrodes associated with the apertures for delivering toner from a toner source to a substrate in accordance with image data. A first voltage source is provided to establish a flow of toner particles from the toner source to the substrate. A second voltage source is provided to establish a control voltage between the toner source and the control electrodes to control toner flow in accordance with the image data. The second voltage source provides a first AC field between a toner source and the control electrodes to permit toner flow and a second, diminished, AC field between the toner source and the control electrodes in order to stop the toner flow.