I know this is long, but may be helpful to some viewers who have trouble getting different layers to match up on the paper, plus a few other tips for printing. I put a heading on each section, so you can pick and choose to read what interests you or not.
Use tape to line up layers
If you put a piece of tape on the left edge of your paper and tape it to the table or another piece of paper, you can lift it from the plate & turn it over leaving the tape in place while you add more to the gelli plate. When you lay the paper down again, it will be in the exact same position on the plate so additional colors won't be offset. If you want to work on 2 prints, you can tape another paper to the right.
Make a reusable registration plate to line up layers
You can make a registration plate that can be used over and over. Cut a piece of cardboard larger than the largest paper you use. Glue two strips of cardboard, each about an inch wide (see the * at the bottom of this post) on top of the large piece of cardboard, at the edges of 2 adjacent sides, creating a right angle with them. The thickness of these strips should be slightly less thick than your printing plate. Add a piece of heavy tape (duct tape, electrical tape, Gorilla tape) on the top of the cardboard strip on the shorter end. Then, from the bottom, add 3 (or more, if that side is long) thin nails or tacks with large flat heads that are long enough to go through your base cardboard, the extra cardboard strip and stick out about 3/8 to 1/2 inch at the top. Space them evenly. Remove the nails and use permanent glue (like E-6000) on them to glue them back in place. After the glue dries, add a strip of heavy tape across the bottom of that area to help hold the nail heads in place.
Making 2 small prints on the same paper using a registration plate
To print 2 prints on the same paper, place your printing plate snugly in the right-angle corner with the short end of the plate against the long end of the registration plate. Place your paper so the nails poke holes in through on the short edge (see the * at the bottom of this post). Lay the paper down over your printing plate and rub. You can remove the paper completely, being careful not to tear bigger holes with the nails, Turn the paper 180ยบ, poke new holes, then print your second print. You can replace the paper on nails for additional colors and it will be in the same place it was the first time.
Making 1 large print using a registration plate
If you have a large plate and want to print only one print on a piece of paper, place the shorter end of the printing plate at the shorter end of your registration plate (see the * at the bottom of this post). If you have a large plate and want to print only one print on a piece of paper, place the shorter end of the printing plate at the shorter end of your registration plate (see the * at the bottom of this post).
How long will a cardboard registration plate last?
A cardboard registration plate should last a pretty long time. You could cover it with a water-resistant coating so you can wipe it clean with a damp cloth. (I use several coats of Min-Wax indoor/outdoor spar urethane, but similar sealants will work.) When I taught school, I had 5 classes of students using c ardboard registration plates for 12-16 days each year and they lasted about 4-5 years. But, you could also make one from wood or maybe thick sturdy plastic that might last longer.