B07 Contrast varnishes and liners for solubility and discuss whether these materials should be used close to the margin of a restoration.
Liners are soluble in oral fluids (more soluble than bases due to their Ca(OH)2 content) and should never cover more than the dentin surface shielding the pulp. Liners are also rather soft. They should therefore never be placed as a thick layer under an amalgam, because they will not provide the amalgam with a good support.