Mounting tissue is a thin, lightweight paper or web material coated on both sides with a heat activated thermoplastic adhesive, used in the dry mounting process to permanently bond photographic prints, artwork, and other flat materials to a rigid or semi rigid support board. It is the intermediary bonding layer in the dry mounting sandwich, positioned between the back surface of the print and the face of the mount board, where the application of heat and pressure causes the adhesive coating to soften, flow, and create a strong, uniform bond across the full surface area of both interfaces simultaneously.
The adhesive used in mounting tissue is thermoplastic in nature, meaning that it softens and becomes tacky when heated to its activation temperature and then solidifies and hardens again as it cools, forming a firm and durable bond that holds the print flat and securely adhered to its support. The activation temperature varies between different tissue formulations and is an important specification to observe, as using a temperature that is too low may result in incomplete activation and poor or patchy adhesion, while a temperature that is too high risks damaging heat sensitive photographic prints, particularly resin coated papers and colour materials that can be susceptible to surface changes or colour shifts at elevated temperatures.
Mounting tissues are available in several formulations to suit different applications and requirements. Standard mounting tissues designed for general photographic and display use are the most widely available type, offering reliable adhesion at moderate temperatures suitable for most conventional photographic papers and mount boards. Low temperature mounting tissues are formulated to activate at reduced temperatures, making them safer for use with heat sensitive materials including resin coated photographic papers, inkjet prints, and other substrates that might be damaged by the higher temperatures required by standard tissues. Repositionable mounting tissues use a pressure sensitive rather than heat activated adhesive that allows the print to be lifted and repositioned after initial placement, offering greater flexibility during the mounting process at the cost of a less permanent final bond.
While mounting tissue and the dry mounting process it facilitates produce a visually excellent and durable result for display and presentation purposes, the permanent and irreversible nature of the heat activated bond means that mounted prints cannot subsequently be separated from their support without risk of damage to the print surface. For this reason, mounting tissue based dry mounting is not considered appropriate for the archival or conservation mounting of valuable, rare, or irreplaceable photographic prints, where reversible mounting methods using conservation grade materials and adhesives are always preferred to ensure that the print can be safely removed from its mount at a later date if required.