An article 7 made from a porous material, such as a ceramic material, is dipped into a liquid impregnating material 12, such as molten urea in a bath 14. After withdrawal from the bath 14, excess impregnating material 12 is removed from the article 6 by means of an air knife 22. The article is carried by a carrier or fixture 6 to be conveyed along the processing line on a conveyor 2. The fixture 6 comprises a lower support 32 in the form of a pair of parallel bars which define between them a slot 38. The fixture also has clamping devices 42 for holding an upper region of the article 7, while the weight of the article 7 is supported by the lower support 32.