Process Focus: Freeze Drying for Art/Documents Restoration
While textiles, electronic items and hard goods get a lot of the attention when it comes to contents restoration, soft goods should not be overlooked either. After all, the likes of books, manuscripts, business records, legal files, contracts, artwork, photographs and more are cherished items too – some in terms of sentimental value and others in terms of business value.
And while ultrasonic and specialty cleaning machines, hand scrubbing, washing and laundering and other technologies and techniques can restore the likes of hard goods, electronics and textiles to pre-loss condition, documents are a little different, especially when it comes to water losses. Like any other contents that have been water-logged, documents need to be dried, too. But how this is done is tricky. You can’t just put books and papers in a drying chamber or ring out the paper.
One of the most popular methods of restoring such valuables in a water loss is a non-invasive process known as freeze drying. Specifically, it removes water from a solid state to a gaseous state, thereby avoiding expansion, sticking and wicking. Here’s a closer look at how it works:
• Documents are packed out and then immediately frozen. This reduces the risk of mold growth and prevents the contents from losing structural form by locking it into a firm position.
• Contents are then placed in a freeze drying chamber, where a high-pressure vacuum removes the air. A vacuum, negative atmosphere lower than the pressure of outer space is then mechanically created inside the chamber – an essential part of the freeze drying process.
• Moisture turns to vapor, which collects on a condensing surface colder than -40° Centigrade. This condensing surface is typically located on the outside of the chamber.
• To eliminate bound water, a heat source is then provided in the chamber to complete the freeze drying process.
Specifically, the freeze drying process eliminates water through a process called sublimation, where a solid (ice) shifts directly into a gas (vapor), completely bypassing the document-damaging liquid state of water. Contents maintain their structure throughout the process, meaning that the condition they were frozen in is the condition they’ll stay in following the process.
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