Sentence:  A leather dressing may brighten the object and give it a 'finished' look, but may not actually contribute to its conservation. Finishes may lead to problems in the long run, so care should be taken. Dressings may absorb dirt and may create a tacky surface. If they contain inappropriate ingredients or if too much is applied these may <WSD>spew</WSD> onto the surface. 
Meaning of the word marked with <WSD> tags:  To develop a white powder or dark crystals on the surface of finished leather, as a result from improper tanning.