By Sibel Ergener
Sellotape: the go-to, easy to use fix-it when there's a tear through the page of your book. Tape, you may be surprised to find, actually causes quite a lot of damage to paper and when brought to a book conservator its removal is a tedious procedure. What exactly does it do when left there long term?
A LITTLE BIT OF BACKGROUND INFO
What is sellotape, actually? How does it work? To start with, sellotape is made up of a few layers.
1. On top there is a clear film, called the carrier, which is traditionally cellophane. Cellophane itself is regenerated cellulose, the stuff that provides structure to plant cells and is also used to make paper and plastic. Nowadays the carrier in clear tapes is generally plastic, but you can find tapes with paper carriers such as masking tape.
2. The bottom layer is the sticky part, the pressure-sensitive adhesive. The adhesive is traditionally rubber-based and is made so that it bonds with what it touches when pressure is applied. When self-adhesive tape was first invented this was a big deal, since before the adhesive would have to be triggered by heat, water, or another solvent.
When a piece of it is ripped off the roll and put on the page, the pressure-sensitive adhesive (or the sticky part) adheres to the paper.
Why is it important to know this? Well, you may notice that when you unwrap a gift the tape just peels off easily, preserving the giftwrap (you might not know this if you tear the giftwrap off, the way I do). The tape was probably attached less than a week before you got it. The rubber adhesive, however, is a long polymer chain just like the cellulose that makes up paper. Over time as the paper and the adhesive on the tape stay stuck together the two types of polymers will begin to interact and attach to each other. This process is called cross-linking, and this change to the chemical structure causes the sellotape to become insoluble and discolored. The longer this goes on, the more difficult it is to remove the adhesive from the paper and the more discoloured it becomes. However, as it cross-links it also becomes less effective as an adhesive and eventually the tape carrier falls off, leaving solid, discoloured adhesive behind. At this stage there's not a lot a conservator can do.
Tape removal is a pretty common activity for book and paper conservators, and here's a quick rundown of how it goes. If the tape is relatively new and has not had time to cross-link extensively, it has a better chance of being removed without leaving discolouration behind.
Here are two examples of tape I have found on separate books:
The tape in the top image still has sticky adhesive underneath the carrier, and the one in the bottom image has solidified. For the bottom image, the process of removing the tape is simply lifting the carrier and then attempting to remove the solidified adhesive underneath mechanically with a microspatula and scalpel without damaging the material underneath. In this situation I could remove some of it, but the adhesive does not always remain on the surface of the paper. Here's an "after" picture for reference:
For the tape in the top image however, the process is a bit longer.
To begin with, I had to remove the carrier from the page. To do this I used a hot air gun to carefully loosen the adhesive and used tweezers to gently lift the carrier as I went along. All this does is warm up the rubber adhesive so that it becomes more flexible and easy to manipulate.
Some adhesive will remain on the page even after the carrier is gone, so it's important to remember to put waxed paper between the pages to prevent them from sticking together if you are going to close the book. While the discolouration and trapped dirt is noticeable, it's a bit hard to capture stickiness in photos, but the shine on some of these may give an idea.
Removing the adhesive is fairly straightforward but a time-consuming process. Since rubber is nonpolar I chose to use heptane to loosen it and remove it, but the decision of which solvent to use depends on situation and conservator's choice and experience. Depending on the amount of cross-linking and the formulation of the adhesive to begin with, other solvents or mixtures of solvents might be more effective. Generally you want to choose the safest solvent available that can still do the job. I did this, by the way, with proper fume extraction and nitrile gloves---don't try it at home.
Using cotton wool wrapped around a bamboo stick, I rolled heptane along the adhesive to remove it.
It will normally take several attempts of rolling solvent over the adhesive to totally get rid of the stickiness. Even when the dirt and stickiness are gone, some staining remained on these pages. At this point it is possible to look into other treatment options to partially or completely remove the staining, but this would have been another long treatment that wasn't viable in the context in this book!
This is only one way of going about doing this. Another option is to make a solvent gel, which holds the solvent in place, exposing the paper to less liquid, but residue may remain on the paper. Your conservator will make the choice depending on various factors, their preference, or their experience.
If the tape was used to hold together a tear, a conservator will go on with paper repair. But remember, if the sellotape had never been there in the first place, they could have immediately gone on to this step, and the paper would still be its original colour!
In the long run, use of sellotape in a book is detrimental for a variety of reasons, so if you have a book with a tear in a page decide on its value to you and your family before reaching for the tape.