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The use of heat and solvent activated tissues are common in library and archives conservation. They are especially useful on materials like brittle wood-pulp papers, moisture-sensitive papers, tracing paper, clay coated papers, mold damaged papers etc. This presentation was part of a joint research project between the Library of Congress, and the National Archives and Records Administration, with the aim of identifying the solvent and heat set tissues that can be safely used on collection materials. The talk included tips for preparing such repair tissues, and case studies showing the use of the different adhesive combinations on a variety of paper-based materials.

The group of pre-coated repair tissues identified by the speakers as safe to use on collections had to have the following qualities:

• Good adhesion/ heat and solvent activation
• Low activation temperature
• Passes the PAT test
• No significant color change or chemical damage to substrate
• Reversibility
• No blocking from carrier side
• Flexible over time
• Maximum translucency

The adhesive and adhesive combinations that passed the testing requirements:

• 1 : 4 | Lascaux 498 : water
• 1 : 1 : 2 | Lascaux 498 : 0.25% methylcellulose : water
• 1 : 1 : 1 : 1 | Lascaux 498 : 0.25% Klucel G : 0.25% methylcellulose : water
• 3 : 2 : 8 | Lascaux 498 : Lascaux 303 : water
• 10% Aquazol 200 in water
• 5% Aquazol 500 in water

 Tips for making and storing tissues:

• Lascaux is difficult to measure so use the displacement method
• Prepare Aquazol 1 – 2 days before you need to use it as it dissolves slowly
• Apply adhesive to Japanese Kozo paper by brushing through the tissue (presenters used machine made Japanese kozo papers 5, 8, and 9 gsm)
• Store the ready-made tissues on silicone release mylar or between sheets of silicone release paper
• Instructions are available on the AIC Wiki: https://www.conservation-wiki.com/wiki/BPG_Adhesive_Recipes_and_Tips 

Tips for heat application:

• 95-120°C depending on adhesive with 2 – 5 seconds dwell time
• Touch briefly with bare iron to position the repair tissue
• Use silicone release paper barrier
• Let cool under weight
• Ethanol can reduce sheen of repair tissue

 Tips for solvent application

• Blotter sandwich was the best activation method
  • Ethanol saturated blotter in polyester sleeve; place strip on blotter and close the sleeve; press lightly; apply to tear

Some comments mentioned in relation to different case study examples:

• The double Lascaux recipe was used to guard books, the tackiness helped in moving things into position, but was not ideal for infills.
• 5% Aquazol on 8 gsm machine made Japanese Kozo was useful for tears on moderately thick paper. However, it was not strong enough for areas that needed to be continually folded and unfolded.
• For brittle wood-pulp papers, the presenters often used 5% Aquazol 500 on 5 gsm Japanese kozo or 10% Aquazol 200 on 5/8 gsm Japanese kozo. The presenters’ colleagues mentioned that they preferred the 500 as the 200 sometimes appeared shiny and visible.
• For mending perforations, 10% Aquazol 200 on 8 gsm kozo activated with ethanol and further activated with heat was used
• For bound volumes, 5% Aquazol 500 on 5g Kozo, as well as Lascaux 498 were good options.

Reversing mends

• Application methods did not affect reversibility
• Ethanol works well; heat does not work well
• Heat set mends are not heat-reversible, do not apply heat set tissues on ethanol soluble media

Conclusions:

• Avanse – Plextol tissues did not pass the test criteria (probably because of Avanse)
• Aquazol 200 and 500 tissues are options if RH is controlled (Aquazol loses tackiness in high RH conditions)
• Ongoing feedback and collaboration is needed from everyone as these adhesives must be continually evaluated
• A comprehensive study will be published