0 01 to 5 microns can be forced by pressure to flow into the porous material some of the particles will become trapped within an aperture or passage 36 thereby reducing its open area and restricting the flow in that area the amount of flow restriction that is achieved is a function of the quantity and sizes of particles 38 trapped in the porous material this can be controlled through particle feed rate particle size distribution driving pressure and infiltration time until the desired permeability is achieved the printing surface 30 may have a durable release coating 46 a material providing a low surface energy effect in its solid or semi solid form may be suitable for use as a release coating 46 on the printing surface 30 for example a plasma coating a coating containing a silicone compound or a fluoropolymer coating may be applied to the printing surface 30 as a release coating 46 as mentioned above the use of such a durable material may not be desirable in some embodiments however the use of such a durable release coating 46 in combination with the extrusion of a release agent or another first liquid may be particularly useful in some embodiments of the present invention in some cases the extruded liquid may in effect cushion or protect the durable release coating 46 and thereby extend.