This is a project I designed for my Cricut Maker 3 machine: it uses a mixture of digital and hand-worked craft skills. If you don't have a digital crafting machine suitable for working with leather, you can substitute in tooling/pyrography and doing all the cutting by hand.

Supplies

undyed veg tan leather: I used approximately 1.2mm thick
dyes in your chosen colours
wide brush: I used a repurposed makeup contouring brush
pipettes
rubbing alcohol and applicator
set square
scratch awl (a tailor's awl will work fine too)
knife that will cut through leather
computer
digital crafting machine and cutting mat
masking tape
leather paints and brushes
leather top coat: I used carnauba cream

Step 1: Digital Design

I decided to make my bookmarks 5x16cm, with five strips of fringing. First I used Cricut Design Space to draw and group the four inner strip cuts - I decided to make two rows of bookmarks, meaning I could make two sets of fringing with one set of cuts. I used the position tool under the 'More' dropdown menu to position my cut lines.

After I'd positioned all the inner short cut lines, I drew three horizontals (top of first row of bookmarks, middle one to separate the top row from the bottom row, and one at the very bottom), and six verticals, to cut my five columns of bookmarks.

As a bonus, I added some debossing patterns for the non-fringed parts of the bookmarks: mermaid scales for the top row, and dragon scales for the bottom. I've not included the instructions for how I made these patterns so as to keep things short, but if you want to know how I designed these in Inkscape, drop me a comment and I'll make a mini tutorial and link it. :) I did two layers of the same debossing designs, so that when I ran it through the machine it would go over the same lines twice for a deeper impression.

I grouped everything and clicked 'attach'.

Note: because of the size and number of bookmarks I chose to make, I needed to use my 24" cutting mat so the leather piece would fit. If you don't have a large enough cutting mat, you will need to adjust how many bookmarks you make at a time (or make the bookmarks smaller).

Step 2: Mark and Rough Cut Leather

For the number of bookmarks I chose to make, I needed a 25x32cm rectangle of leather. I added around 3cm extra each way, so used my scratch awl and set square to mark out 28x35cm. I then cut this out with my clicker knife (because this is quite thin leather, you shouldn't need a particularly heavy duty knife).

Step 3: Dye!

This was a fun bit. First I wiped down the leather with rubbing alcohol (this cleans off any grease, and aids dye penetration). Then I put the leather aside, and started prepping my brush. I used the pipettes to drop dye onto the brush, making a rainbow. I created horizontal lines of colour across the shorter side of the leather, adding more dye for each pass, and flipping the colour order by turning over the brush (so it should go red-orange-yellow-green-blue-purple-blue-green-yellow etc.). If you want completely bright and clear colours and are doing a large area, I'd recommend washing the brush off once or twice, and starting with a fresh dye job. I decided to just let the colours blend, so they did get a little bit muddier by the time I reached the end.

I let the leather rest overnight, to make sure the dye was completely dry.

Step 4: Deboss and Cut

I opened up my Cricut Design Space file, and clicked 'Make'. I adjusted the position of the project on the virtual mat, and positioned my leather on the real mat to match. You want a border of around 1cm on all sides of where the bookmarks will actually be cut, but you don't want to go over the edges of the marked grid, or the machine won't load.

Once I'd positioned the leather, I taped the edges down and put pressure all over to make sure it was stuck down well.

Going back to the laptop, I clicked through to the next screen. I set my base material to 'Tooling Leather - 6-7oz. (2.4mm)'. This is a thicker leather than I was actually using, but I've done a lot of experimenting with the standard and custom settings and different kinds of veg tan, and this is the only one that gives me consistently good results. I'd really recommend doing a few experiments of your own with your machine and leather, before committing to any big projects.

I put the debossing tool into the machine, and moved all the little guide wheels over to the side (you'll need to do this every time you switch from using paper or vinyl to something thicker like leather).

Important next stage: all this debossing and cutting takes a while. I went and made a cup of coffee, and fetched my spinning, to have something to do.

Once I was settled in for the long haul, I went ahead and loaded the mat, and started the debossing.

A long time later, the debossing finished and looked great. I loaded the knife tool and set that off too. Because it was set to heavy weight leather, the machine planned to do 16 passes. But with leather half the thickness, I found it was completely cut through after 8. Around about pass 7 I paused the machine to check its progress, then let it go ahead and do 8. Then I paused, checked again, and unloaded the mat.

The leather curled a bit as I took it off the mat, so I let it flatten under a weight overnight.

Step 5: Outlining and Painting

I used a pen filled with black leather dye to outline the debossed scales on each bookmark. In future I'll also experiment with a) automating this using the Cricut machine, and b) playing around with products that will get into the debossed bits, and wipe clean on the raised bits.

I then mixed up some leather paint with a touch of mica powder, to make it pearlescent, and painted some random scales. I left it to dry for a few hours.

Step 6: Top Coat and Done!

Finally I gave each bookmark a coat of carnauba cream. You can use whatever top coat you like, but bear in mind that anything oily might damage your books.