Agar gel loaded with micro-emulsion could be used to extract lipophilic materials from porous surfaces. The physical properties of the gels are good enough for a conservation work. They allow the micro-emulsion to flow on the porous surface and to wet it but maintain the micro-emulsion in its structure and prevent the formation of rings. https://www.roneverhart.com/FlasKap-Madic-Liquor-Lid-for-Large-Tumblers-9-ounce-Color-Options/