How to make a niche in an altered book

Supplies from left clockwise: Wax paper or Press and Seal (preferred), neither of which is needed if you are starting with an unaltered book, gel medium, old paint brush, clamps, clothespins, rubber band, self healing mat, cutting tool with removable blade, ruler, object to go in niche, book, either altered or unaltered.

Measure the tallest point of the object to be placed in the niche.
Measure that same amount, or a few more pages, for your block of pages which will become your niche.
Place a rubber band around the excess pages and bend the book all the way back, thus causing a nice crease in the book. This will help hold the pages up when you start gluing. DO NOT do this if you already have pages in the book that have been altered. Allow me to repeat: SKIP THIS STEP if your book already has altered pages.

Place "Press and Seal" (from now on referred to as cling wrap), wax paper, or freezer paper between the last page of the book and the inside back cover. To be honest with you, I've never added a niche to a book that was not already partially altered. So, I use the wrap, because I clamp the glued pages to the cover and I don't want glue to get on the back cover during the drying stage. Then, I hold the decorated pages upright, so the block of glued pages, which will become the niche, don't shift or get distorted, or dry in the wrong place relative to the back cover.

However, I found that when I started with an unaltered book, it was easier to stand the block of glued pages straight up and keep the pages I had banded flat. That means I didn't need the cling wrap, or any other substrate that would keep the block of pages from sticking to the cover.

So, the general rule of thumb, when making niches like I do, is to use the instructions as I've photographed them if the book is unaltered, and follow the instructions until it comes to drying, then clamp to the back cover and support the altered pages, keeping them at a 90 degree angle from the table.

I have to admit, if there's any way you can make your niche before you decorate any pages, you'll have a much easier time.

Secure the excess pages with a rubber band and stand the book on one end.
Place one clamp toward the top of the outer edge, as shown in the photo. Using an old paint brush, run the gel medium along the entire top edge of the book.
Make sure you have good, even coverage of the gel medium. If necessary, smooth with your fingers.
Remove the side clamp and place enough clamps along the top so it is secure. If you get too much gel medium in some areas, the clamps will cause the gel medium to ooze out. Remove the clamps, smooth or remove the gel medium, then reclamp.

Now that your top is glued and secured with clamps, add one clamp at the bottom corner for stability. Run gel medium along the outside edge of the block of pages.
If you click on the picture for a larger view, you will see a bit of gel medium has spilled onto the front of the pages. Also, the gel medium on the edge is not even.
Use a paper towel to clean any excess gel medium from the front and to smooth the gel medium along the edges. If you allow the gel medium to harden, it will leave a blob that you might have to sand after it has dried.

Remove the clamp from the bottom and clamp the side. Make sure the clamps are close to the top and not too far down on the page to achieve a good bond.

Glue the bottom of the block of pages. Pay careful attention to the area nearest the spine and the corners. Be sure the block of pages is upright. I knew my coffee mug would come in handy for something besides holding my yummy beverage.

Alternately, if your book has completed pages, you will want to band them, then prop the banded pages up. At this point, you will need to clamp the glued block of pages to the back cover and you will need to have a piece of wax paper or the cling wrap between the glued block of pages and the cover.
Clamp the bottom of the block and give it a final inspection before the gel medium begins to dry. If any of the clamps are causing bulges, unclamp and move, or add more clamps to correct the problem.

Note how the corners are well clamped as is the area closest to the spine.

When your block of pages is completely dry, remove the clamps, keeping the pages straight.

Apply gel medium a second time. This time the block of pages will be easier to handle, since they are now a single piece.
It's hard to see, but there is a bubble directly under the "e" in the word "bubble."
Be sure there is ample glue in that area, then clamp directly over the bubble.

Try to clamp in places you didn't clamp before so the outer edges don't end up with ripples.

Once your block of pages (also known as the niche) is dry, remove the clamps and place a self healing mat between the back cover and block of pages. Remember, I wrapped the cling wrap around the back cover, but you will not need to if you are able to keep the front of the book upright during the gluing process.
This shows the block of pages, self healing mat, cling wrap, and back cover in that order.
Clamp the block of pages to the back cover, making sure to catch the self healing mat in the clamps.

If you want to put your object behind a window, you will need to remove the first page before the niche (block of pages) and clamp it to the block of pages. I chose not to enclose mine, so I put the page back under the rubber band. By not gluing the blog of pages to the back of the book, you will still have the option to cut a window from this page from the back, if you change your mind.
Place your object on the page in its final spot. Using your ruler or a straight edge, draw lines for the window. Leave enough room for your object to fit comfortably in the niche. Remove the object and begin cutting, one side at a time.

I've just started the cutting process. Remove cut pages as you go. It will be much easier than if you saved them till the end.
As you can see, I'm about half way through the window in the niche. To get square corners, I first cut one line (say the top line) one direction, then turn the book and cut the same line the other direction. That seems to keep the corners square, at least for me.
I'm finally through to the self healing mat. This process can take a long time, so don't get discouraged.

One of many arguments for not gluing the niche to the back cover, is that you can really clean up the edges and the corners. Although the irregularities won't show after you have your decorative papers glued on, if you really want perfection, use a nail file/buffer to smooth them.
When you feel your cuts are smooth, apply gel medium to the window. If there are some ragged edges, the gel medium will help level them out. This is the trickiest part of the entire process, because you have to fiddle and adjust the clamps until they fit in the window without distorting it. Be sure to get into, or close to, each corner, and as close to the edge of the window as possible.
Make sure you keep the niche in an upright position while the window is drying.
When completely dry, remove the clamps, repeat the gluing and clamping process, then allow to dry overnight. When completely dry, decorate the back outside and inside covers, then add decorative papers to your niche, wrapping the papers around to the back of the niche. Glue the niche to the back cover. Clamp as before. Keep the front portion of the book straight as before until the niche has completely dried.

This is an example of a double niche I created for my Money AB. The top window has a covering on it, the bottom one does not.

You can see I decorated the back cover before I glued the niche in place, thus giving it a finished look.

In this view, you can see that I wrapped the decorative paper (actually a paper towel) around the back of the niche before I attached it to the back cover. I had a thinner vial when I measured for the lower niche, then changed my mind, so this vial protrudes more than I would have liked.

If you have any questions, feel free to ask.