Adhesives and Consolidants

• Paraloid B-72 (ethyl methacrylate co-polymer, formerly called Acryloid)
• Butvar B-76 (polyvinyl butyral, or PVB)
• Butvar B-98 (polyvinyl butyral or PVB)
• McGean B-15 (polyvinyl acetate or PVAC, formerly called Vinac B-15)
• “White glue” dispersions and emulsions (e.g. Elmers, Rhoplex, Lascaux)

• Various brands of epoxies (e.g. Devcon, Epo-Tek)
• Various brands of cyanoacrylates (e.g. Aron Alpha, Paleo-bond)

• Duco cement
• Elmer’s glue-all
• Five minute epoxy
• Cellulose Nitrate polymers (e.g. Glyptal)
• Model airplane glue
• Ambroid
• Natural organic materials

• Shellac
• Gum arabic
• Animal protein glues

Most preparators do not use precise percentage formulas when making batches of solution adhesives.  This is often because people prefer to ‘go by feel’. Concentrated stocks are diluted as needed especially as solvent evaporates from open containers often requiring the addition of solvent while working.  Some estimates though are given here as helpful starting points.  

Butvar B76

• Adhesive: generally not used as an adhesive
• Consolidant: 2% to 10% (grams/ml) in acetone or ethanol

Butvar B98

• Adhesive: generally not used as an adhesive
• Consolidant: 2% to 10% (grams/ml) in ethanol

McGean (formerly Vinac) B-15 

• Adhesive: around 30% (grams/ml)
• Consolidant: ranges from about 1.5% to 9% (grams/ml) in solvent. Or make up a 16% solution to dilute as needed.

Paraloid B-72

• Adhesive: 20-30% (grams/ml) in acetone or 1:1 acetone:ethanol up to 50% (grams/grams).
• Consolidant: range from around 2% to around 10% (grams/mls) in acetone or ethanol. Or make up a 15% stock solution to dilute as needed.

Paraloid B-48N

• Adhesive: 50% (grams/ml) in acetone
• Consolidant: generally not used as a consolidant

Primal/Rhoplex WS24

• Adhesive: generally not used as an adhesive
• Consolidant: between two-five parts WS24 to one part water 

To make up a solution adhesive that comes as a pellet resin (e.g. Paraloid B-72 and others):

• Determine the appropriate percentage by weight of adhesive and volume of solvent
• Measure out the adhesive resin pellets and place them in a square of cheesecloth and tie off into a small bundle with cotton thread. 
• Suspend the bundle in the jar of solvent (ensure that the jar is big enough to accommodate the bundle without overflowing)
• Leave for several hours or overnight (The adhesive will flow out of the cheesecloth and into solution without forming a solid lump on the bottom of the jar which is hard to break up.)
• Drain and remove the cheesecloth bundle. 

Alternatively, the measured adhesive can be poured into the solvent and a magnetic stirrer used to agitate the solution until it has fully dissolved.  This technique is more successful for Butvar B-76 than the method above.

Cabosil (fumed silica), glass microballoons and cellulose powder can all be used to bulk adhesive solutions. Used in small amounts they provide a bit of body to the solution.  In larger amounts they can be used as a gap filler that can be easily manipulated with solvents or a heated spatula tool.  The different shapes of the flat polygonal silica particles and the round glass microspheres or the irregular causes each to bulk the solution in a slightly different way and some people prefer the working properties of one over the other. Cabosil is also sometimes used as a matting agent to reduce the sheen of an adhesive coating on a specimen.  Some preparators also use cellulose powder or marble dust for either bulking fills. 

The use of cyanaoacrylate accelerators such as sprays for an instant bond is not recommended because of their commonly observed tendency to turn fossils bright green, yellow or blue, reportedly in reaction to iron. Additionally, these accelerators are potential health hazards. Moisture alone will speed the setting of cyanoacrylates so just blowing on a join can speed its set time to seconds.  Paraloid B-72 in acetone is very tacky and can “grab” fragments even faster than cyanoacrylates and should be considered a good substitute for quick assembly of joins. 

The easiest adhesive to identify is shellac which, under ultraviolet light has a characteristic orange fluorescence. Other adhesives tend to fluoresce a bright whitish with a purplish tinge that will reveal their presence but is not diagnostic.  Some clues can also be gained from solubility tests – i.e. using foam-tipped or cotton wool swabs in various solvents or by shaving off a small sample and putting it in a glass watchglass with drops of the various solvents.

Shellac was, for many years, thought to be the best material available for consolidating fossils. It was used extensively for this purpose from the 1850s through the 20th century and, while it is still used even today, is now widely considered an inappropriate material for fossil preparation due to its ageing properties.  Over time, shellac yellows, becomes brittle, attracts dust, and cross-links becoming insoluble and difficult to reverse. With better choices now available to conservators there is little reason to use shellac.  

It is impractical and dangerous (to fossils and preparators) to try to remove shellac from an entire fossil collection. Attempting to remove any consolidant or coating from a fossil may do more damage than leaving it in place. Reasons to remove an old coating include:

• Noticeable deterioration (i.e., peeling, shrinking, flaking, spalling)
• The need to expose obscured features for research purposes
• To improve the aesthetic appearance of a displayed specimen
• To effect a proper repair if a previous join has broken

Aged shellac can be very difficult to remove.  While the material is normally soluble in ethanol, once cross-linked it can be virtually insoluble.  Techniques used in removing shellac depend a great deal on the nature of the specimen. Small, fragile specimens and bone actually being held together by the shellac require considerable care. Larger, more robust material is somewhat easier to deal with safely. Remember, though, that you will only be able to remove surface coatings; shellac that has penetrated the interstices of the bone cannot be removed. Surface buildup of shellac can be removed from “sound” bone as follows:

Materials:

• Ethanol/Acetone 50/50
• Poultice material i.e. cheesecloth, gauze, clean cotton rags or Viva paper towels
• Light-weight polyethylene sheeting
• Small (< 1/2 inch blade) wood, polyethylene, Teflon, or steel tools 

Method:

• Apply an ethanol/acetone-moistened pad of cheesecloth to a small area of the fossil. Cover with a piece of polyethylene sheeting. Let this remain in place for about five minutes, then remove and examine the surface coating. The shellac should have softened enough to gently scrape (“coax” is a better word) some off. Quite often, the shellac surface will bubble up and slide off very nicely, especially on smooth, non-porous bone. Repeat the procedure as needed to soften and remove all the shellac on the surface.
• Residue can be wiped off with solvent- moistened cheesecloth. You may also try applying the ethanol/acetone mixture to the bone and covering directly with polyethylene sheeting (no cheesecloth). The idea is to keep the surface coating of shellac exposed to the solvent, but to avoid soaking the bone and risking collapse.

NOTE: Many of the materials used in the preparation and conservation of fossils pose serious health hazards. Always acquire and read the Material Safety Data Sheets for the materials you use. Do not use any hazardous materials if you lack the facilities or training required to use them safely.

As with removing shellac, it is important to first assess the stability of the specimen to ensure that it can withstand this process of adhesive removal.  Most epoxies can be softened using a heat such as a “Masters Heat Torch”, “Milwaukee Variable Temp Heat Gun” or other brand.  These tools generate high heat and should be used with extreme care both for the safety of the operator and the fossil. When heating resins, it may also be advisable to wear a respirator if there is not adequate localized ventilation. Cyanoacrylates may be swollen at a micro-level by solvents making mechanical removal easier.