Mary-Kate and Ashley Olsen are moving higher and higher into the world of fashion.

The Olsen twins have become successful with designing careers and opening the Elizabeth and James store in Los Angeles. In Tuesday's report from People, the girls dished on their work and how special it is to focus on vintage items.

"There's something nice about knowing you are the only person in the world who has it," Mary-Kate said. "It's sort of like buying art. For everything that we call modern today, think about pieces made in the '20s and how modern they looked then and now."

Ashley added that "quality and scarcity" are the qualities that define exquisite fashion.

"You look at these pieces and you have an emotional reaction, not just because they are pretty objects, but because they look and feel different from what is possible to do currently," she said.

Working with each other in this career is really what makes the Olsen twins grateful to be a part of it. Mary-Kate said that Ashley is "loving and consistent" while Ashley had something sweet to say back to her sister. No matter what happens, these two are closer than ever.

"You are the most grounded, brutally honest and compassionate person," Ashley said. "And my best friend."

The girls are big fans of other fashion icons, including Coco Chanel and Mariano Fortuny, but Mary-Kate explained why it's better to not meet them face to face.

"Sometimes you don't want to meet them," she said. "For me, it's interesting to see how different designers have affected other houses throughout the years. When you look at the work of John Galliano or Karl Lagerfeld, it changes your perspective of a house."