CO2 Dry Ice  Micro-Dusting

     Many of us in the conservation fields are now somewhat familiar, in theory, with CO2 Dry Ice cleaning.  For micro-dusting with a fine mist of granulated ice particles, a large solid block of CO2 dry ice is placed into the machine.  With the added pressure from the auxiliary air compressor, the ice block is continually shaved down to a fluffy, powdery snow.  This is then forced through the hose and nozzle at extreme speed and controlled pressure between 10-300 PSI (depending upon the particular model of the commercial machine that is used the PSI range may go higher). We averaged between 35-60 PSI. The nozzle comes with several attachments to vary the shape and spread of the spray. 

     The common adherents for removal that we most often use this application in conservation approaches are: Rust/Corrosion, Adhesives/Residues/Films/Oils, Plants/Lichen/Algae, Rot/Earth/Clay/Sand.  However, CO2 Dry Ice cleaning can also be utilized to remove surface Mold/Microbes/Bacteria.  The frozen CO2 gas will easily and gently remove all surface flora and blooming sporulating materials.  We use this approach for large outdoor sculpture, and murals.

     Dry Ice Dusting has many superior and unique benefits over other more traditional media and cleaning treatments.  It is non-abrasive, non-acidic, nonflammable, nonconductive, and is an environmentally responsible approach with no secondary clean-up of additional material waste, other than that which was removed from the object during the sublimation exposure and micro-shock wave.  There is no water to reclaim, no solvents or other chemicals involved, no heat or transfer contaminants to contain.  In the end we have a technology and treatment phase that is cleaner, faster, and safer than many of our traditional mechanical and chemical based solutions—with far fewer risks to way in the balance.

     Surface cleaning with below freezing dry ice has been utilized in industrial manufacturing for sometime, and in recent years the softer less invasive or aggressive use of small granules, or shaved blocks has begun to be adopted into the field of conservation science. The application of this treatment is relatively simple to perform, control and minimal equipment is required. A mixture of compressed air, CO2 and CO2 dry ice particles are directed through a hose attachment with an adjustable nozzle to control the area of space that will be diffused. The dusting particulate is propelled towards the surface at an extremely high speed, with an initial temperature of -78.5c. As the CO2 dry ice explodes across the debris field and soiled surface, a thermal shock reaction occurs, causing any unwanted materials to shrink, expand, loosen and quite literally fall away. This instant temperature change sublimates the ice particulate crystal into gas before it reaches the underlying object substrate, transferring minimal kinetic energy upon impact. The gas has 800 times greater volume and spreads out underneath While this treatment approach is not ideal for all mediums and materials, as some weak objects cannot withstand the initial force, similar to the volume air pushed from a hairdryer. 

     There are many varied applications for which it will be extremely useful in our multidisciplinary fields. CO2  dry ice dusting will both remove and kill active blooming surface mold growth.  For previous projects, we have used CO2 dry ice dusting successfully to surface clean the unfinished back sides and interior aspects of antique furniture cabinets, and drawers, stone sculpture, and 100’s of volumes of books.  This method and application would not be an appropriate treatment for with most paintings, some painted surfaces and some fragile textiles.

     The metrics for describing the results of such treatment approaches can be lengthy are fairly sophisticated.  The overall conclusions are less surface abrasion, related to the removal of all matter of contaminant soiling and debris having been cleared.  Compared with other traditional methods of mechanical clearance and removal, such as: the soot sponge, hand tools, scalpel and other brushes.  We have found in certain circumstances, dry ice was better at preventing abrasion, especially in dealing with 3-D textured surfaces with contours, edges and crevices.