The following is recommended by Matheson as very effective : - 30 gal. of coal tar, fresh, with all its naphtha retained; 6 lb. tallow; 1 1/2 lb. rosin; 3 lb. lampblack; 30 lb. fresh slaked lime, finely sifted - mixed intimately and applied hot. When hard, this varnish can be painted on by ordinary oil paint if desired.