I have a bunch of pretty good books on it - some flowers you have to take apart and press each petal separately. I'll try the vandas a few different ways and see what works best.
i had AMAZING good luck with silica gel. i had a vanda tailor blue that preserved rather well. the color came out almost true to the color, maybe even a little bluer. same with oncidium sweet sugar. theyve been my only attemps so far that came out nice.
the trick is to use the flowers right before theyre going to die so they have reduced water but still in their original shape and form. when the lip starts to show some veining. i only had problems with some of the crystals being hard to remove but because i microwaved them. i think if i was patient and left them in the sand for a week in room temp theydv come out nicer.
wait i tried a phal and the lip swelled up in the microwave. it looked odd but because the fleshy part was too full of moisture. it was also white so it came out more transparent than id like. i think the same problems that apply to normal dry flowers apply here. the flatter the better, the less textured drier flowers, and some colours do better (i.e. yellows/pinks/blues not reds)
using a microwave press, with very short bursts and cooling time in between, I was able to press and dry some of the flat orchid flowers (vanda, miltonia, etc) with 100% success and color fidelity! I am super excited and am going to pursue this much much further.
It perfectly preserved the tesselations on the vanda I tried, which is what I was hoping for!