These gels have other advantages: they bear enough body so that no remnant of it is left after use, which does not happen with other much common gels[1. There is a difference between gels, thickeners and viscosity modifiers, The American Institute for Conservation AIC wiki is a very good online resource about it.] (hydroxypropyl cellulose -Klucel®-, methyl cellulose, etc., that remain partially or totally embedded on the support, depending on how we use them).
And they are reusable! They just need to be rinsed in distilled water in order to be used again. We can soak them in the most suitable solvent (whether it is organic or hydrophilic, of course), use them, and then wash them and keep them in the appropriate solvent (distilled water in the case of hydrogels, and a non polar solvent in the case of organogels).
The application in the conservation field is obvious: removing tide-lines and stains, or apply particular solvents in the most controlled way, either for tape removal or other purposes (and later on I’ll get back to tapes).
It is a pitty that the organogel is not yet available, because for aqueous solutions there are plenty of gels, thickeners and further stuff, but for whatever related to solvents one is always wishing there were more options.
Microemulsions and solvents
We also tried microemulsions, using gels as a medium. These are transparent, unlike normal emulsions that are milky or cloudy, since the colloidal dispersion happens in the microscopic level (among 5 and 150 micrometers). “Normal” emulsions is most of the acrylic polymers, or mayonnaise, which seem to be a single liquid but it is actually a colloidal dispersion of more than one, where each of them has opposite polarity, like water and oil, in the case of mayonnaise.
I am sure that sooner or later I will find a practical application for microemulsions, but I must admit that I don’t see in them such a wider range of application as for gels, for the simple reason that they have a surfactant, which is the one that coheres and allows this colloidal dispersion of immiscible liquids. I guess that there will be particular occasions in which the microemulsion will be of great use, but in my opinion we must differentiate them clearly from ordinary solvents, which simply evaporate leaving no remnant at all. The surfactant in the microemulsion could somehow remain in the artwork, or at some point even react -unnecessarily- with it or any of its components. And, precisely because colloidal dispersions are not stable in the long term (the conforming liquids curdle, separate back) these microemulsions are sold in two different components that need to be mixed, and which have a limited shelf life once they are prepared.
The main advantage of the microemulsion is that it can be much more efficient when it comes to swell or remove certain compounds, since the microemulsion bears different solvents which should not be miscible normally and each of them has different polarity. These different polarities offer more chances to be akin to the compound we need to remove.
The one we had the chance to try was Nanorestore Cleaning® Polar Coating S, that can be also referred as EAPC because it is formed by Ethylene Acetate, Polypropylene Carbonate, 1-Pentanol and water. It also contains an anionic surfactant, Sodium Dodecyl Sulphate (SDS) but if you click on the link you will see that there are other microemulsions with non ionic surfactants (such as Nanorestore Cleaning® Polar Coating B, or MEB, meaning de Methyl Ethyl ketone and 2-Butanol), non polar (to clean waxes) and more varieties.
But the gels can be used with whatever solvent we want, it doesn’t have to be a microemulsion. In the practical exercises we used diethyl carbonate ((C2H5O)2CO), for instance, besides from water and others.
And I must mention that NanoRestArt has considered very much the safety by design of these mixtures, taking good care of our environment and health for potential users. A gauntlet of tests has disregarded the most contaminating/toxic proportions, so that the resulting product has acceptable toxicity levels (as long as its use is the appropriate).
Pressure sensitive tapes: removal from paper
Let’s focus: the goal of all this chemistry and products was to better remove the damn tapes. And Antonio Mirablie made a fantastic summary about their composition:
As we can see, there are two main adhesives: acrylic and rubber based (rubber can either natural or synthetic, like masking tape).
And regarding the backings we find fabric, paper and plastic. Well then, in plastics there is a classification that matters especially, which is porous backings (acetate based, like the translucent MagicTape®) against non porous backings (polypropylene based, or either vinyl and others, which are usually glossy). And why sorting by porosity of the backing? For practical reasons: porous tapes will allow the solvent to swell the adhesive, even when applied through the backing, whereas the rest will not. And another very important reason: porous backings will melt in acetone. If our goal is to make the tape disappear, it’s OK, but watch out if we need to keep it! Even when wanting to remove the tape, it is not wise to leave the support impregnated with this plastic… it is better to remove it mechanically in advance, avoiding its swelling/melting.