There’s a fantastic freeware tool named knobman to create your own knob, faders and more to use in Usine. Here a little step by step tutorial to import and use them in Usine Hollyhock.
Use the menu: file /open/samples/LineShadow.knob (.knob files are knobman files here)
On the right window you test it, and you ‘ll see that this knob has 31 frames.
Now use the menu :file/export image file/, name your knob as you want, this will save a png file.
Load a knob in your patch, in its settings panel, click on image file and load your png file.
Set frames count as 31 (here it’s an vertical one, so nothing to change)
Disable show knob, show caption . You can also use the option bottom text if you keep the value visible. Now, unlock it / re-arrange the size of your knob / lock again.
In the settings panel, clicks on the snapshot icon and choose a name. Now you can see this snapshot when you edit the layout of a knob. You only have to click on this snapshot to assign this layout to your current knob