{"id":28459,"date":"2026-09-28T20:14:19","date_gmt":"2026-09-28T17:14:19","guid":{"rendered":"https:\/\/artrestorationsupplies.gr\/?p=28459"},"modified":"2026-09-28T20:14:23","modified_gmt":"2026-09-28T17:14:23","slug":"paraloid-b72-odigos","status":"publish","type":"post","link":"https:\/\/artrestorationsupplies.gr\/en\/paraloid-b72-odigos\/","title":{"rendered":"Paraloid B-72: a user guide \u2013 solutions, solvents, ratios, reversibility"},"content":{"rendered":"

The Paraloid B-72<\/strong> is perhaps the most widely used synthetic resin in cultural heritage conservation. It is used as a consolidant, adhesive, protective coating and isolating layer on ceramics, stone, glass, metals, wood, wall paintings and archaeological finds. In this guide we bring together the practical information a conservator needs in the laboratory: its chemical nature, which solvents it dissolves in, which proportions are usually used, how to prepare the solution correctly and what \"reversibility\" means in practice.<\/p>\n

Important: the concentrations given below are indicative values frequently found in the literature and in laboratory practice. Every object is different; always test on a small, inconspicuous area or on a sample, and document the treatment.<\/em><\/p>\n

What Paraloid B-72 is<\/h2>\n

Paraloid B-72 (formerly also known in Europe as Acryloid B-72) is a thermoplastic acrylic copolymer of ethyl methacrylate (EMA) and methyl acrylate (MA)<\/strong>, in a ratio of about 70:30. It is supplied as clear, colourless pellets that dissolve in organic solvents. Its glass transition temperature (Tg) is given as around 40 \u00b0C, which gives it a balance between hardness and flexibility at room temperature, but also means that it softens at high temperatures (e.g. in display cases heated by lighting or during summer transport).<\/p>\n

Its wide acceptance is mainly due to its its chemical stability<\/strong>: in ageing studies (R.L. Feller and later work) B-72 is classed among high-stability materials, with minimal yellowing and a limited tendency to cross-link, so it remains soluble for many decades. Key articles on its use are those by S. Koob (1986, Studies in Conservation<\/em> 31) on bonding archaeological ceramics, and Podany et al. (2001, JAIC<\/em> 40) on its use as a structural adhesive and as a \"barrier layer\" within joins. Extensive documentation is also found in C.V. Horie, Materials for Conservation<\/em> (2nd ed., 2010).<\/p>\n

Solvents: which one to choose and why<\/h2>\n

B-72 dissolves in ketones, esters, aromatic and chlorinated hydrocarbons, while in alcohols it dissolves more slowly and with limitations. The choice of solvent is not a detail: it determines the evaporation time, the depth of penetration, the gloss of the final surface, the likelihood of \"bubbles\" or blanching and, of course, the conservator's exposure to vapours.<\/p>\n

Acetone<\/h3>\n

The most common solvent for bonding. It evaporates very quickly, so the adhesive \"grabs\" soon \u2013 ideal for ceramics and glass, where we want the fragments to stabilise quickly. For deep consolidation, rapid evaporation can cause the resin to migrate to the surface and create gloss.<\/p>\n

Ethyl acetate and mixtures<\/h3>\n

Slightly slower than acetone; useful when a little more working time is wanted. Mixtures of acetone with ethanol or ethyl acetate are often used to adjust the evaporation rate.<\/p>\n

Toluene and xylene<\/h3>\n

Slower aromatic solvents that allow deeper penetration and a more matt result when consolidating porous materials. However, they are significantly more toxic; in many laboratories they are replaced wherever possible. Commercial ready-made solutions (e.g. Lascaux solutions) are often based on toluene \u2013 always check the composition in the safety data sheet.<\/p>\n

Ethanol and \"green\" solvents<\/h3>\n

In pure ethanol B-72 dissolves slowly and the solution may be cloudy; it is usually used in mixtures. In recent years, less hazardous solvents have also been examined, such as dimethyl carbonate<\/strong>, which dissolves B-72 and has a more favourable safety profile than aromatics. As with any change of solvent, tests are needed for drying behaviour and surface effect.<\/p>\n

Typical concentrations by application<\/h2>\n

Concentrations are usually expressed as % weight\/volume (w\/v)<\/strong>, i.e. grams of resin per 100 ml of solvent. The values below are the widely published orders of magnitude:<\/p>\n\n\n\n\n\n\n\n\n\n\n
Apply<\/th>\nTypical concentration<\/th>\nComments<\/th>\n<\/tr>\n<\/thead>\n
Consolidation of porous materials (stone, ceramics, mortars, wood)<\/td>\n2\u20135% w\/v (often 3\u20135%)<\/td>\nMultiple low-concentration applications rather than one concentrated one; avoid gloss and sealing the pores.<\/td>\n<\/tr>\n
Consolidation of paint layers \/ flaking<\/td>\n3\u201310% w\/v<\/td>\nDepending on the substrate and the sensitivity of the paint to the solvent.<\/td>\n<\/tr>\n
Protective coating for metals, isolating layer<\/td>\n5\u201315% w\/v<\/td>\nOn metals, often with a corrosion inhibitor added as appropriate; test for gloss.<\/td>\n<\/tr>\n
Sizing primer for porous edges<\/td>\n5\u201310% w\/v<\/td>\nReduces absorption of the adhesive and makes future separation easier.<\/td>\n<\/tr>\n
Adhesive (ceramics, glass, stone)<\/td>\n10\u201320% as a thin adhesive; up to 40\u201350% w\/v as a thick adhesive<\/td>\nHigh concentrations in acetone correspond to the \"adhesive in a tube\" described by Koob.<\/td>\n<\/tr>\n
Resin in fill materials<\/td>\n~20\u201340% solution mixed with glass microspheres or other fillers<\/td>\nLight, reversible fills; adjust the density during application.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Ready-made solutions (e.g. 10% or 50%) can be diluted with the corresponding solvent to reach the desired concentration. Calculate on the basis of the solids content: for example, 10 ml of a 50% solution diluted to a total volume of 100 ml gives about 5% resin.<\/p>\n

How to prepare the solution \u2013 step by step<\/h2>\n
    \n
  1. Weigh the resin<\/strong> on a precision balance. For 5% w\/v: 5 g B-72 in a final volume of 100 ml solvent.<\/li>\n
  2. Use a glass container<\/strong> with a good seal (not plastics that may be attacked by the solvent). Note on the label the resin, solvent, concentration and date.<\/li>\n
  3. Alternative \"tea bag\" method:<\/strong> place the pellets in a fine cloth (e.g. tulle or gauze) and suspend it in the solvent, so that they do not stick to the bottom of the container. Dissolution is more even.<\/li>\n
  4. Allow time.<\/strong> Complete dissolution can take from a few hours to a day, depending on the concentration and the solvent. Shake periodically; do not heat flammable solvents.<\/li>\n
  5. Check the solution<\/strong> for clarity. Cloudiness may indicate moisture or an unsuitable solvent.<\/li>\n
  6. For thick adhesive<\/strong> (40\u201350%), the process is slow; some conservators add a small amount of fumed silica to improve workability, as described by Koob. Storing it in aluminium tubes or tightly closed glass bottles limits evaporation.<\/li>\n<\/ol>\n

    Application: practical tips<\/h2>\n

    Consolidation<\/h3>\n

    Apply with a brush, syringe, dropper or spray, starting with a low concentration. Penetration improves when the surface has already been wetted with pure solvent. After each application, remove the excess from the surface with cotton wool lightly moistened with solvent to avoid gloss. For archaeological ceramics with salts, desalination comes first \u2013 the resin must not \"trap\" soluble salts.<\/p>\n

    Adhesion<\/h3>\n

    The technique that prevailed after Koob (1986) is as follows: prime the edges with a dilute solution (e.g. 5\u201310%), allow to dry, then bond with a thick adhesive (40\u201350% in acetone). A thin layer and correct alignment are more important than the amount of adhesive. Joins need support (e.g. in a sand tray) until the solvent has evaporated from inside the join \u2013 which can take several days with solid, non-porous materials such as glass.<\/p>\n

    Fills<\/h3>\n

    Mixtures of B-72 with glass microspheres (glass bubbles) give light, workable and reversible fills, particularly on ceramics and glass. The proportion is adjusted empirically until the desired texture is reached (from \"paste\" to \"dough\").<\/p>\n

    Reversibility: what it means in practice<\/h2>\n

    B-72 is considered reversible<\/strong> because it remains soluble in the same solvents in which it was applied, even after decades. In practice, however, reversibility relative<\/em>:<\/p>\n