We had mixed results from the glass fusing with ferns.
Good news is that two of the techniques worked really well, the other 7 didn’t.
Without going into too much detail, unsuprisingly ferns by themselves turn to ash at glass melting temperatures. This can be used to create interesting fossil type effects as on 3 above, but at the risk of also creating large bubbles if you don’t use slow temperature ramps. If the fern is delicate then, as on sample 2 above, it is likely to completely disappear.
The key appears to be use glass powder stuck to the fern, as on 1 and 8 above, with a 2 stage process to reduce bubbles, as on 8.
8 is therefore my method of choice to produce a fern in glass. Using this methodology, next comes the large piece I need for the oak carved tray I am making. I just have to hope that the method scales up.