Did the painting have the power to cause people to fall in / out of love? No
Could any storyline involving the painter have achieved the purpose of showing off this set? Or did it have to be a storyline about Carol and Tony breaking up, specifically? Plotwise they could have done just about anything. But for the logistical non-plot reason, this was a choice that made sense.
Okay, it seems that interest in this has fizzled so here is the answer:
Carol and Tony broke up because of the way Dark Shadows was filmed at the time. Like some other soaps of the era, a Dark Shadows episode was filmed in its entirety as if it was in front of a live audience. Editing was an expensive luxury not in the budget. So if an actor muffed their lines, or the boom mike cast an inadvertant shadow, or a vampire put their fangs in wrong, it showed up that way in the episode. Supposedly they even figured in the commercial breaks into the filming and paused for just that length of time. One time a serious fire broke out on the set and the characters continued their scene while the crew doused the burning studio.
Anyway, the story called for witch Angelique to be aging rapidly. Her nemesis had commissioned the clueless but talented painter Sam to slowly age a pretty portrait of the witch from a young woman into an old hag. For some supernatural reason not fully explained, that slow aging of the portrait also would age the witch character. So because Carol and Tony were the actors available that day, they had a long tearful break-up scene. This gave the actress X plenty of time to get all her aging make-up applied, so that she could appear at the end of the episode as having rapidly aged from the start of the episode.
The whole lengthy break-up scene was just a production delay so the “X” actress would have time to be aged for the final climactic scene in the artist’s studio. Otherwise the scene was unimportant to the plot.
Really all I was looking for was that the break-up scene was there so that another character could exchange costume and make-up. Today that would not happen outside of live drama, but in the days of early TV it was almost like live drama. Watching the episode now it is strange to think how different putting on a daytime TV drama was in the past.
If you will indulge me, here is another lateral thinking problem on a similar issue:
On Dark Shadows in 1967, Sam Evans, an artist, is rendered blind by witch Angelique, supposedly so that the painter can never again paint a portrait to age the witch. It is also an act of revenge by Angelique. The character of Sam Evans would remain blind for the remainder of his time on the show (a few months later he is killed off). However, none of the plot reasons had anything to do with why the character of Sam Evans became blind. The actor who played Sam Evans was David Ford. And he specifically asked the shows writers to blind his character and they complied. Why did David Ford want his character on the show to become blind?
Did he proactively request it for reasons of his own (reasons that had nothing to do with the show)?
Did he suggest it as a solution to a problem that had arisen on the show, maybe behind the scenes?
Did he proactively request it for reasons of his own (reasons that had nothing to do with the show)? It had to do with the show.
Did he suggest it as a solution to a problem that had arisen on the show, maybe behind the scenes? Yes.
was the fact that the glasses hid his face an important aspect?
For example (but not limited to) did David Ford have to play two characters and the glasses allowed for some camouflage from the audience perspective….or maybe he was a twin, and it was a way to distinguish the blind twin from the other.