26.1 Chemistry and Research – Regalrez or Regal Varnish?

12/05/11

Five years ago Regalrez 1094-based varnishes turned up in the market, since then we have collected several case studies and valuable work experience in the field of the restoration. Let's see what the situation is. 

The good reputation for Regal Varnish and the ' not so good' one for the ketones-based varnishes (such as Laropal K80), need some more discussion.

Let's keep in mind that Regalrez 1094 is an aliphatic compound (the molecule feature in
 the pic) characterized by a low molecular weight (~900 uma). It is is produced by polymerization of vinyl-toluene and alpha-methyl styrene, followed by hydrogenation. Hydrogenation makes the polymer stable because the saturation of the double bonds means elimination of the weak spots where degradation (the aging process) starts.
Refractive index of the resin is pretty high (1.519) and the small size of the molecule chain confer to it low viscosity and '
leveling' ability. These two factors make its optical properties similar to those ones of the natural resins like Dammar gum.

Stability proofs

In the CTS article titled “Polimeri sotto esame” (= polymers under investigation) we talked about the findings reported in the thesis dissertation “studio delle resine sintetiche impiegate nell'arte contemporanea” (= study of synthetic resins in contemporary art), University of Pisa [1]. The research confirmed that Regalrez 1094 molecules do not have any polar groups.

Gas chromatography–mass spectrometry (GC/MS) mainly detected dimers, trimers and low molecular weight oligomers.

FTIR e GC/MS analytical methods showed aging of Regal Varnish develops through oxidation of Tinuvin 292 at first, followed by the forming of carbonyl groups (C=O) and a double bond (C=C) in the ring of cyclohexane. Those chemical reactions had been examined by FTIR during the first 'Italian' case-study on Regalrez 1094 (after the basic research conducted by De La Rie and others [2][4]). An investigation through high energy UV radiations carried out by Maria Camaiti at CNR-ICVBC [5], revealed the protective effect of Tinuvin 292. Those data plus the removing trials done by Paola Mariotti on natural seasoned samples [6], represented the first step to the birth of Regal Varnish, at the end of 2005. Oxidation of Regalrez 1094 was detected as well by Fabio Talarico Studio in 2008 [7] through an accelerated aging process (UV radiations). Calorimetry measures provided more information about the limited yellowing of the substance and the stabilizing effect of Tinuvin 292 (FTIR reduced peak of carbonyl group at 1700 cm-1).

The enemies of Regalrez
Like every substance, Regalrez 1094 has some specific limits that need to be considered before varnishing. We should not ascribe the responsibility of an unsatisfactory result to the resin without knowing all the potential enemies involved in that process. Therefore it is important to bear in mind the following characteristics.

Regalrez 1094 is easily reversible in low polarity solvents 
– Although this characteristic is one of the strength points of the product, we have to make sure there is not a similar solvent still 'imprisoned' in the layers of the painting. In fact, the solvent of the varnish may call the old molecules of the previously used solvent back to the surface.
The evaporation of the solvent evolves especially in the cracks, giving rise to the so called 'orange rind' effect. This undesired effect may occur when the restorers:
1- 
cleans with solvents characterized by high retention
2- applies a varnishing retouch with solvents characterized by high retention
3- retouches after diluting pigments and resin with solvents characterized by high retention
By 'solvents characterized by high retention' we mean high weight aromatic molecules such as turpentine oil and amyl acetate and ethyl lactate and dipentene and many others.

It is well known that turpentine essence is the most likely to be retained in layers of seasoned oil and that at some specific concentration levels it is not released at all.

Luca Dori and Daniela Piacenti [8] demonstrated that turpentine oil is not compatible with Regalrez. Due to the reversibility in low polarity solvents(, Regalrez cannot be used as retouching varnish, especially for classic techniques. Special expedients are required for these kind of applications; for example the adoption of Gamblin colors dissolved in isopropyl alcohol.

Regalrez 1094 is made of tiny molecules- 
This means a very good leveling ability and high level of penetration, especially in the porous substrates. When dealing with areas spoiled by previous aggressive cleaning operations (the so called 'prosciughi'), Regalrez 1094 tends to 'disappear', so it cannot be used in this step.
We strongly recommend to saturate those particular areas with mixtures of Tylose or Klucel in alcohol...another choice could be Gustav Berger’s O.F. Isolating PVA Spray Varnish, that has been conceived for sustaining retouching operations (after that another varnish coat is required)
According to those considerations, it is clear that Regal Varnish has to be considered ideal as the 
final varnish.

As reported during several technical meetings, Regal Varnish formula can be modified by using other products of the CTS catalog.

Here are the weight percentages:

Regalrez 1094                 23.0
Kraton G-1650                  2.0
Tinuvin 292                      0.5
Petroleum essential        
74.5
oil D30 
(not denaturated)     



Regal Varnish Mat
 contains 3.5% of micro-crystalline wax Cosmolloid 80.
It looks paradoxical that in the field of varnishes and new formulations a basic lab test such as 'accelerated aging' is often neglected.
Since 2004 We have tested a lot of varnish grades to collect evidences and support the publications: thanks to the patience of many restorers willing to test and apply our different formulations.



References
1_ Orsini S.; “Studio delle resine sintetiche impiegate nell’arte contemporanea”, Thesis Dissertation, Chemistry Degree (2010)
2_ de la Rie E.R.; McGlinchey C.W.; “New synthetic resins for picture varnishes” in 
Cleaning, retouching and coatings, Ed. Mills & Smith, London (1990), 168-173. 
3_ Berns R.S.; de la Rie E.R.; “Exploring the optical properties of picture varnishes using imaging techniques”, Studies in Conservation 48 (2003), 73-82.
4_ de la Rie E.R.; “Why use a sinthetic picture varnish?”, in 
Art et Chemie: les polymères, Paris(2002), 63-68 
5_ Borgioli L.; Camaiti M.; “Stabilizzazione di polimeri per la verniciatura di dipinti”, Conference “Colore e conservazione”, Thiene (2004) 
6_ Borgioli L.; Mariotti P.; “Applicazione di nuove vernici ad alta stabilità”, 2
nd National Congress IGIIC, Genova (2004), 470-476. 
7_ Talarico F.; “Proprietà delle vernici idrocarburiche e prospettive”, Kermes 72, October-December
 2008, 70-73. 
8_ Borgioli L., Dori L., Piacenti D.; “
Effetti della temperatura e dei solventi su vernici sintetiche e naturali” Lo stato dell’arte 5, Cremona, 11-13 October 2007

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