There are few cult props in the history of cinema as famous as the Grail Diary from Indiana Jones and the Last Crusade. This instructable details how to recreate a (story) version of this prop. While challenging to create - you'll need (to learn) book binding and weathering skills - it results in a very cool item for cosplay purposes or as a display & conversation piece.

First, you'll need to decide whether to make a “Hero" or "Story" version of the diary:

Hero version: contains (only) the exact pages as used in the movie prop, with the same pages repeated multiple times in a set order and very specific pages/details/inserts added in certain places so as to be 100% faithful to the movie prop.
Story version: logically reorders the pages from the movie prop and extends them with invented pages and inserts, in order to fill any gaps and tell a consistent story from cover to cover - namely the full journey of Dr Henry Jones Sr to find the Grail.

In my case, I opted for the Story version because it is a more realistic representation of what the "in universe" diary would have been like and it can actually be read as a consistent story, even though it may not be an exact replica of the production props used on set. If you prefer to make a Hero version, you can check out this instructable instead.

Supplies

A computer and printer (preferably a laser printer to avoid the risk of ink washing out while weathering, though an inkjet will also do if you're careful)
Printer paper. This can be standard 90-120 gsm white paper, as well as some sheets in various thicknesses and colors for the inserts
Cardboard for the cover
A sheet of (real or faux) leather for the cover. You may be able to recover a piece from an old jacket/bag/pair of boots/... instead of buying a new sheet
Ruler, sharp knife and scissors
PVA glue
Cotton thread and a needle for the binding
Mull (bookbinding gauze) or alternatively some cotton or linen fabric
A clamp and a book press or alternatively some heavy books/objects
Black elastic band (e.g. from Aliexpress)
Blue watercolor paint and brush
Brown wrapping paper
Flax cord

Step 1: Obtaining the Diary Contents

There are several options for obtaining the contents of the story diary:

Gather the texts, images and inserts yourself from various sources such as Zenseeker, Club Obi Wan forum, RPF forum and the books the drawings in the original props were sourced from (Grail: Quest for the Eternal and The Flowering of the Middle Ages) as well as screenshots from the original movie and documentaries. This requires a significant amount of research and editing, but allows you to tailor the story as you please and for e.g. manually write out the pages in actual handwriting.
Print Celeste Conway's free story grail diary and inserts. This is a great beginner's version, though I found the font quite hard to read. Also, the resolution of certain images is quite low and there are quite some typos in the text.
Acquire a ready to print bundle (such as this one on Etsy) with a fully revised text, a font that mimics Henry Sr's handwriting and high resolution pages and inserts.

Step 2: Printing the Pages

Pre-made digital bundles generally come formatted in printable signatures. A signature consists of single sheets of paper that each contain 4 book pages (2 on each side). Pages printed on a signature sheet may look out of order and upside down, but the pages have actually been carefully arranged on the sheets so they will appear in the correct order and orientation once the sheets are printed, folded, bound, and trimmed. If you're creating the contents yourself, you will need to convert the individual pages to signatures. This can be done using the free program Bookbinder 3.0.

The pages will need to be printed out in duplex (on both sides of the paper) with printer options "flip on long edge" and printed in "actual size" (so no "Fit to Page", "Scale to Fit", "Crop to Fit" or similar option checked). They can be printed on either A4 format or US Letter size format and then be cut down to size along the crop marks. Standard weight (90-120gsm) printer paper is fine. It's best to do a test run of a few pages to validate that everything is setup correctly before printing the entire run.

Once all sheets are printed, cut and folded, group the signatures (see image for an example diagram of the page ordering per signature) and double check that all pages are in the correct sequential order.

Step 3: Weathering the Pages

Pages can be weathered by dipping them into (and/or spraying or brushing them with) strong coffee or tea. This gives them a realistic aged look. This short video illustrates one easy way of aging the paper:

https://www.youtube.com/watch?v=rBcD-8QSWpw

The pages can easily tear while wet, so be careful when handling them.

Next, you can dry the pages in an oven (on low heat), in a microwave or using a hair blower.

Once dry, the pages can be straightened by placing them between two sheets and ironing them with low heat (to prevent the ink from transferring).

Step 4: Binding the Book

Now it's time to bind the signatures together into a textblock. This involves making a template to punch holes in the right places for the binding stitching.

The process of sewing the text block, gluing the spine and adding the end papers is explained well in these videos, so I will not go into detail here:

https://www.youtube.com/watch?v=Ec5UThbybSA

https://www.youtube.com/watch?v=dBk2LA_Ofso

Instead of mull, you can also use cheese cloth or some other cotton or linen piece of fabric.

Step 5: Making the Cover

To reinforce the leather for the cover, cut out 2 cardboard sections which are just slightly larger than the page size and one spine section which is the size of the textblock spine width (see image). Use PVA glue to glue them in position on the leather, leaving a few mm room between the sections so the cover can be easily folded closed, as well as enough leather around the edges to fold over and glue inwards over the cardboard. Weigh down the cover while the glue is drying.

The process is illustrated in this video:

https://www.youtube.com/watch?v=ExCAqtTbD7I#t=5m10s

The flysheets can be created by printing out 2 sheets in a marbled design, cutting these to twice the size of the diary pages, folding them in half and gluing one half of the first to the left inside cover and one half of the other to the right inside cover.

Step 6: Making the Inserts

The inserts can be printed on different types of paper (and in some cases envelopes) to create some variety in the look and texture. Reference photos of the originals are available on Zenseeker.

When printing the images, be sure to check and where necessary adapt the print size. Some high resolution images may need to be scaled down. Below is an overview of the approximate sizes:

LARY tickets: 20 x 5 cm (7.87" x 1.97")
Quote inserts: 10.6 x 17. 6cm (4.14" x 6.93")
French bank note: 18.5 x 11.4 cm (7.20" x 4.37")
US Dollar Silver Certificate: 7.9 x 18.9 cm (3 1/8" x 7 3/8")
Insurance envelope: 12 x 4 cm (4.75" x 1.5") depending on how much you rip off the top
Cigarette pack size: 15.2 x 8.5cm (6" x 3.5/16")
Eastern telegram: 21.5 x 17.0 cm (8 1/2" x 6 ¾")
Tablet rubbing: 41 x 58 cm (16" x 23")
The heights of the Arabia and Venice maps can be aligned with the heights of your diary pages.
The photo's and several other inserts are invented props, so there is no official/correct size reference in the hero prop. You can choose what seems right to you and/or use the above mentioned video for reference

The grail tablet tablet rubbing is the only insert which due to its size cannot be printed on a home printer (at least not in one piece). If you have access to a 3D printer, the best option is to create an actual 'rubbing' by printing this free 3D template and following the instructions on that web page. If you have no access to a 3D printer, you could have the original image printed at a professional print shop on A2 size paper (or slightly scaled down on A3 size paper)

Some of the inserts are glued into the diary, while others are loosely placed between specific pages (see video for the locations).

Step 7: Finalizing the Book

Some of the original pages have blue coloring applied. You can see pictures of the original pages on Zen Seeker. This can be reproduced using some blue watercolor paint.

If the leather used it too clean looking, you can make the diary look well traveled by staining it with coffee, adding scratches using sandpaper,... Some methods of aging leather are explained in the following article:

https://curtidosmenacho.com/gb/blog/news/how-to-aged-leather-complete-guide-to-an-authentic-finish

Finally, we can add a black elastic band and recreate the wrapping using some brown wrapping paper, prints of the Venice stamps and label, as well as some flax cord. If you have a 3D printer, you can use this model to recreate the ink stamp: https://www.printables.com/en/model/393553-venice-italia-stamp-for-grail-diary

And there you have it... a real life grail diary :)