Quote 19
"There is something fatal about a portrait. It has a life of its own." (9.13)
Dorian's views on his portrait have clearly changed since it was new. He now thinks of it as a reminder of his own mortality, rather than a promise of his eternal youth. There is something disturbing about seeing his own image start to decay before his eyes.
Quote 20
As the door closed, Dorian put the key in his pocket and looked round the room. His eye fell on a large, purple satin coverlet heavily embroidered with gold, a splendid piece of late seventeenth-century Venetian work that his grandfather had found in a convent near Bologna. Yes, that would serve to wrap the dreadful thing in. It had perhaps served often as a pall for the dead. Now it was to hide something that had a corruption of its own, worse than the corruption of death itself -- something that would breed horrors and yet would never die. What the worm was to the corpse, his sins would be to the painted image on the canvas. They would mar its beauty and eat away its grace. They would defile it and make it shameful. And yet the thing would still live on. It would be always alive. (10.6)
The portrait appears to have taken on a kind of revolting, zombie-like quality – it's both deathly and alive at the same time. In Dorian's mind, it's both a reminder of his life (in a creepy way) and the slow, corrupt death of his soul.
Quote 21
Hour by hour, and week by week, the thing upon the canvas was growing old. It might escape the hideousness of sin, but the hideousness of age was in store for it. The cheeks would become hollow or flaccid. Yellow crow's feet would creep round the fading eyes and make them horrible. The hair would lose its brightness, the mouth would gape or droop, would be foolish or gross, as the mouths of old men are. There would be the wrinkled throat, the cold, blue-veined hands, the twisted body, that he remembered in the grandfather who had been so stern to him in his boyhood. The picture had to be concealed. There was no help for it. (10.14)
Now that one change has revealed itself in the picture, Dorian feels its mortality growing more and more pressing. He feels doomed on its behalf, and terribly afraid of the changes that will come to pass. His fear of age and death is evident in this truly revolting description.