So what I did was I took the original image (I used GIMP to do this) and I took the image I wanted to use, put a white background on it, and desaturated it. Then I messed with the levels to make the thing I wanted to have transparency around it completely black. I then inverted the colors and had a transparency map which I could then use in the opacity input on the material (once I had set the material to transparent)
(Make sure you mess with the shading model to get the right shading for your thing, for me I had to change it to subsurface profile as you can see on the bottom left under where I changed the blend mode to translucent)
Unfortunately, I was limited to uploading images, so just don’t forget, anything that shows as black on the image will be the transparent part. In the end, however, I never kept the original transparent into UE4
