PVA is a better choice for archeological ceramic, bones or wood mainly because the repaired surface is required to be untreated or untouched. The bonding principal of PVA is that it soaks into porous materials such as old ceramic, bones, wood, etc. For best adherence strength and longevity, use the proper PVA viscosity (V15 or V25 for porous ceramic).
Resin epoxies are a better choice for all nonporous materials and porous materials that require complete restoration (fillers and coloring). See more details on material used
We are often asked which adhesive is the best for pottery or ceramic restoration? Generally, our answer is Resin Epoxies or PVA (Polyvinyl Acetate). Either choice can be selected depending on your objective and the material of the repaired item.
The benefits of PVA (Polyvinyl Acetate) are:
1) Will not yellow and has good stability to light (UV)
2) The gluing job can be reversible meaning, the glue will remain soluble and can be easily removed from a repaired subject later and be ready for re-gluing.
3) Easy to work with and easy to clean up
4) Low cost
The disadvantages of PVA:
1) Medium bonding strength (way less than new modern epoxies)
2) Cemented item can fail in humid, cold or hot storage
3) Will not work with non-porous objects
4) PVA shrinks and therefore will: a) distort repaired objects with thin walls and b) the repaired gap will be recessed a bit after drying
5) When dry, can leave a shiny outer surface which can be eliminated by wiping the surface with a lint free cloth saturated with PVA solvent (e.g., acetone).
We use mostly epoxy resins because:
1) Most projects that come our way use non-porous ceramic that makes PVA not suitable
2) Most projects we work on require complete restoration including color retouching. We use acrylic base finishing that will not discolor. Therefore the discoloring properties of epoxies is irrelevant.
3) Epoxy does not shrink as it cures
4) Epoxy has extremely strong bonding qualities
5) Epoxy does not chemically interact or effect acrylic finishing
6) Epoxies come in various options in terms of curing time and colors
7) Epoxies can be a filler and is workable (drilling, sanding, polishing)
1) Almost all will yellow with time and can be an issue with restoration that does not require color re-finishing. Non-yellowing epoxy is very expensive, requires precision to use, and hard to get. Note that even "non-yellowing" epoxies will yellow when exposed to UV light for long duration although the efect will be slight.
2) Removing epoxies is difficult and therefore is not considered "reversible"
3) More expensive
4) Managing mixing two parts can be messy and wasteful
5) Tooling and working surface clean-up is more labor intensive
6) Strong smell and potential health issues when applying
As a general rule, epoxy resins should be avoided for archeological restoration. However, epoxies are occasionally required by conservators because nothing else has the needed bonding strength. Resin epoxies are excellent when a very strong and permanent bond is required. Resin epoxies are a better choice for all cases where the repair can be hidden and the only good choice for nonporous materials such as high fired ceramic, metals, glass, etc.
IMPORTANT: Ceramic restoration materials are not food safe, liquid or heat proof (over 190 degree F) and repaired items should not be used on cooking or food serving ware more...
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