I have just found a moon map published in the UK newspaper The Daily Mail from 1969, which I saved because of the first moon landing and an abiding interest in astronomy. However, it's been folded up for the past 50 years, and was published in two parts, which I sellotaped together at the time. Obviously it's now in pretty poor shape, but I want to preserve what's left as best I can (it's still readable!) I've bought acid-free conservation paper as a backing, and a very large acid free conservation 'plastic' envelope to hold it, but I want to stick the two parts together, on the backing, to show the whole map. Can anyone recommend the best adhesive or method for doing this, please?
I'd be tempted to have it laminated (it would take a big roll laminator; schools, libraries, or print shops may have them and the cost would be nominal). As long as the paper is exposed to air and humidity, it will continue to deteriorate. It will eventually become brittle. Laminating it will keep it together in its current condition and allow you to handle it and examine it up close without worrying about it starting to fall apart. It may be possible to laminate the sections into one continuous piece, or the sections could be laminated separately and mounted next to each other. After lamination, you can mount them for display, and will have a lot of flexibility in the type of adhesive.
In paper conservation usually a wheat starch paste (not wheat flour!), rice starch paste or methyl cellulose is used as a glue. As backing paper Japanese Kozo paper is the gold standard today because it has very long fibres (is very stable over time) and is semi-transparent and acid-free. Other paper types can be used as well, as long as they're acid-free. To conserve newspaper a heat set tissue is recommended because it's easy to work with.
Please keep in mind that conservation is an art of itself and conservators need special training to avoid accidentally damaging the object they want to conserve.
Wash your hands before touching the paper. If you have sweaty hands or need to work on the paper for an extended time, wash your hands again periodically.
This video shows the process of conserving a brittle and torn piece of paper. (I found that playing the video at 1.25x playback speed makes it easier to understand the speaker.) You can use the same technique to merge the two parts together and mend any torn edges. The general goal is to keep the object in it's original state as much as possible. That's why documents aren't usually completely backed with paper, but only in fragile and damaged areas.
If you want to frame your paper, make sure to use UV filtering glass in the frame, because light itself also damages paper.
The reason why I strongly advise against backing the whole page with paper is not the conservation standard of retaining the original state, but the curling of wet paper.
I'm sure all of us experienced this problem as children: cover a large area of paper with a wet glue, stick it to a dry piece of paper and the result will be an ugly curly or wavey mess. As adults we might have experienced that strips of wallpaper were aligned perfectly while wet with paste, but ended up having gaps between them once they dried.
That's because the fibres of paper soak up water and expand when wet and shrink back to their original size when dry.
So if you cover the backing paper with glue paste and stick it to the newspaper, either the backing paper will end up wrinkled or it will damage the newspaper when drying. The same applys to covering the newspaper with glue, only that the risk of physically damaging the paper is even higher.
Backing the entire newpaper page with heat activated tissue might be an alternative, but only if the print survives the heat without being smudged or faded. You also risk literally roasting the paper (causing it to get darker brown and even more brittle) when you apply too much heat.