A "Grotesque Prestidigitation"

One of Angel's responses to Tess' wedding night confession was that there had been a "grotesque prestidigitation." The implication was that he'd been duped into marriage by Tess’ clever deception. In the fire lit room in a mansion with just the two of them it's initially puzzling that Angel would use the word prestidigitation, which Tess surely didn't know, instead of words expressing the same meaning she would have understood. The answer may be telling.

In his phrase "grotesque prestidigitation" he's really not talking to Tess but to himself or some imagined body in his mind. Being a conformist to his society's standards and now in a situation where he finds his wife, marriage and plans suddenly at odds with society's approval, he's desperate to exonerate himself and remove himself from the "intolerable" situation. It's as though he's saying, "I've been scammed. I’m a victim. Don’t blame me, it’s her fault." From this moment through most of his time in Brazil, he continues in this attitude.

After months in Brazil he briefly comes across another Brit to whom Angel discloses his troubles at home. The fellow responds that Angel's made too much of Tess' blemishes and that others in similar situations have accepted, understood and had happy marriages. In a fairly short time Angel reforms his thoughts and returns to Tess as soon as he’s able.

While many suggest Angel's mind has been broadened, more likely the stranger simply convinced him society's judgment on Tess wasn't as harsh as he had thought. Angel isn't more broadminded, society is. What the story reveals is that Angel puts society's judgment ahead of his own, if he has any. What's essential to Angel is society's judgment he's a respectable man, and to keep that reputation he's willing to sacrifice his marriage and even Tess. Whatever Angel does, in his mind society's jury is constantly judging him. Where Tess sets nothing above her love for Angel, Angel sets nothing above conforming to society's judgment. He'll be the same with Liza-Lu and all the others in his life.

Angel is deeply deluded about women. He expects them to be two extremes: either a prostitute or model wife. He thinks he has rejected the influence of his strictly Christian upbringing, but really he hasn't the guts to do so. As you say, Angel has no real personal principles. He has some lofty ideas which Tess mistakes for an individual mind. Tess is very much an individual with her own personal code of morality but she cannot find a like-minded person.