cavity using a jet of particles having at least hardness 7 that are forced through a resilient pvc mask which protects the surfaces of the slab that are not intended to be sandblasted using the pvc mask allows obtaining a rather deep cavity in the slab without having to frequently replace the mask due to wear and also allows obtaining cavities with edges that have contour lines that are essentially identical to the contour lines of the windows in the mask utilization of pvc masks impart to the cavities conspicuous artistic appearance thereby beatifying the appearance of the ornamental slab then the slab is made an ornamental slab by incorporating two and or three dimensional ornamental elements into the cavity then the cavities are covered with a covering sheet for protecting the ornamental elements residing therein the covering sheet is made of a desired material which may be transparent or semi transparent and may have different shapes and colors application_number US 57211404 A description fig1 is a sectional view of an exemplary ornamental slab according to the principles disclosed in the present invention ornamental slab 10 comprises e g stone 11 in which cavity 12 is cut preferably by sandblasting stone 11 ornamental element 13 best shown in fig1 b is secured in cavity 12 by utilizing supporting elements 14 the proximal end of supporting elements 14 in this example a total of three supporting elements is adhered 17 to bed 15 of cavity 12 by utilizing corresponding adhering agent e g epoxy resin then ornamental element 13 is put in its place in cavity 12 and adhered 18 to the distal end of supporting elements 14 covering sheet e g made of glass 19 is then put against the open side.