There are several (in addition to the tinfoil one someone else mentioned). You can use plaster, scupting it before it sets completely, then painting appropriate colors. You can use artist's gesso, or acrylic gel medium (my favorite). Again, you may need to paint appropriate colors. A very glossy clearcoat after final painting helps.
Thick paint can be used in 700 scale. Put down a coat of base paint, then "paint on" wave crests with the brush. In that scale they do not need to be very high. Two or three coats are enough. You do the gesso and artist's mediums the same way, but in larger scales the ridges (wave crests) need to be much higher, so you need the stiffer stuff.