How do I apply a colour line gradient across a whole piece, not just each individual lines in a piece?

The most simple solution in my opinion:

1. Select all the Elements that should have the gradient-border
2. Set the border-color the desired gradient
3. Press "G" to select the gradient-tool
4. Click-drag the gradient in the desired direction
5. enjoy

Hope this helps and is still relevant for you!

I'm not sure I understood you correctly - but.

You can prepare first row of your thin artwor and then another / last row with stroke adjusted

Then try tu use Blend Tool (W) - just click first grouped row and then secend (lte last grouped row). In beetween you can see as many rows as it's possible. It's difficult to explain in English.

Pawel

It would probably be easiest to first group all your objects

Then create a rectangle with the gradient, put it below all the other objects.

Then select both and in the transparency panel "Make Mask"

You will probably need to Invert the mask with the button.

Note that this method is not suitable for all production methods as it won't e.g. create a path for cutting. But it will be suitable for printing.