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Correct exposure of the highlights... What creates the illusion of 3D on white objects is a very delicate interplay of the 255 specular values (i.e. the sparkle on the pearl) and the overall tone of the solid white object. The texture of the fabric and the angle of the lighting also play a role in the perception of the surface texture.
Many photographers equate "pure white" with 255 when perceptually a 255 is best reserved for specular reflections such as those in the highlights of the metal buttons. You can use Levels to examine what if anything is clipping here:
Copy the image, open in Levels and hold down the alt/opt key and click the highlight slider and you'll see the rendering above showing the clipping in colors of representing RGB channels. If you then move the highlight slider to the left it will force darker shades of tone to clip similar to what will happen with overexposure. In this image you need to push the highlights down to around 230-255 to get the entire white tunic to clip in all channels. The 0-256 range represents the range of the sensor so each 35 units is about equal to one stop of sensor sensitivity. So that means the "white" of the tunic is about 3/4 to 1 stop under "pure" clipping white.
If you were to shoot an actual pearl and expose it so it looked natural, or draw one in photoshop...
you'll find a similar range of tonal values give it the "pearly" appearance. What makes a pearl look different than a white glass bead is that a pearl has an irregular surface with "tooth" that will create very subtle modeling. In the two illustrations above I added some noise to the second to simulate the same micro-texture. The texture of some fabrics, especially polyester blends that catch specular reflections will create similar modeling if overexposure or flat lighting doesn't obliterate it.
Just get some white fabric and practice controlling your lighting and exposure and you'll be able to get similar results. When capturing the image in the camera you need to anticipate how the highlights will change during editing, in particular the 16-bit editing gamut > 8 - bit sRGB JPG step. If you start with an exposure that is perfect OOC in the RAW by the time you make the JPG you will lose those subtle differences in the highlights. With a bit of experience you will learn how much "Kentucky windage" you need at capture to compensate for the workflow changes. To retain them in the JPG you need to start with a RAW file that is about 1/3 stop under what seems perfect, convert to JPG then adjust as needed.