Laropal A101 of the BASF. The alternative could be the Laropal A 81, always of production BASF, but this last one has a range of softening of 80-95°C respect has 95-110°C of the Laropal A101 that above all guarantees so a less sticky surface in warm climates. Moreover the A101 has a minor retention of the solvents, for a faster drying.
The Laropal A101 is soluble in alcohols (buthyl, isopropane,…), esters (ethyl-lactate, ethyl-acetate etc), ketones (acetone, MEK, aromatic etc), hydrocarbons (toluol, xylene, etc). It is instead insoluble in aliphatic hydrocarbons (white spirit, hexane, etc) present in great part of varnishes, so assures the impossibility “to move” the retouching during the phases of final painting.