One voxel cannot have both transparent and nontransparent parts. However this trick is possible if you place two objects on the same spot.
Here's an example:
![Posted Image](https://cdn.discordapp.com/attachments/418522033500979206/862059073397588018/scr-test2.map-0000.png)
However, this trick only works for custom maps.
And this is how I voxelized jars:
![Posted Image](https://cdn.discordapp.com/attachments/418522033500979206/862044304280780850/blud0000.png)
It's a compromise I was willing to take.