He is accused of violating four women, aged 14-18, during 2014 and 2015 at his private Auckland studio.
A video interview with one of the women was played to the court today.
She said she told friends what the artist was doing with her, but was concerned about notifying others.
"They said, 'You have to tell him to stop'. He was just doing it all the time.
"I didn't know if they were going to support me or if they were going to look at me like, 'You're disgusting'."
But, she said, "things just started getting worse".
"Every time you would go in the room he would always lock the door.
"You need this experience, it will make you a better arts student," the woman said the artist would tell her.
He also said to the teen if she allowed the physical relationship to continue she would begin to "see colours" and be better able to express herself through her painting, the court heard.
"You need to get used to this, I'm going to take you on a journey and you'll be better at arts," she said the artist explained.
The teen said the artist also described oral sex as "like giving you the energy".
"I'll deliver my energy to you, and you're able to let out your bad stuff," she said the artist told her.
"I believed him, I trusted him. He knows everything. I had to obey him, because I had no choice - I thought he would help me."
She said the artist would give her a lolly after their lesson and asked her to "pretend nothing happened" when she left the studio.
Hamlin said many people, men and women, have come to his client for arts tuition.
"He denies any touching he had was inappropriate or without consent," Hamlin told the court in his opening statement today.
"The relationship he developed with these complainants went on for not only days, not only months, but for years. He thought they were willing participants."
Hamlin said his client "believes honestly" that when there was a sexual relationship it was "obvious" it was consensual.
"He is an innocent man."
The artist denies the allegation of underage sex "completely" and the accusation that he assaulted one of the girls with a belt, Hamlin said.
The trial continues.