A uniform, homogeneous and well-behaved, cool APP suitable for industrial processing of materials is generated between two opposing parallel-plate metal electrodes if the opposing face of one or both electrodes is covered by a glass sheet and a high voltage is applied across the inter-electrode gap. The area of the electrodes and, hence, the plasma can extend to m2 but the gap between them is, typically 3 - 20mm. The applied power is Radio Frequency, typically 10-100kHz and linear or other transformers are used to step up the voltage applied to the electrodes to, typically, between 5 - 25kV. If the applied power is in continuous wave mode, the precursor gas must be dominantly Helium, but, if the applied power is pulsed, other gases can be used. The plasmas so generated are a powerful tool for the surface engineering of industrial materials in a continuous, on-line mode.