Abstract: A hollow structural glass block is slotted by cutting or grinding to allow the installation of a specifically sized decorative panel insert into the interior of the block. The decorative insert is preferably comprised of stained, iridescent, or etched glass. A bead of clear silicone rubber caulking is applied to the bottom edge of the insert prior to slipping the insert through the slot. The silicone rubber caulking functions as an adhesive to secure the bottom edge of the insert stationary to the bottom interior of the block. The top edge of the insert is positioned between the edges of the block defining the slot. The slot, and the top exposed edge of the insert lying therein is covered with a layer of clear silicone rubber to secure the insert and seal the interior of the glass block against the entrance of moisture and mortar. Additionally, substantial thermal insulating values are maintained in the decorative blocks due to the sealed nature when completed.