Medium format film moisture-proofing and backing paper degluing treatment: Customs travel film self-sealing bag packaging and electrostatic spark prevention

1. The structural fatal flaw of 120 film: backing paper and bare roll without cassette

Unlike 135 film, which is tightly wrapped in a tin cassette, 120 film uses a fully open reel structure:

1. Backing Paper hygroscopic hydrolysis disaster:

• There is a strip of highly absorbent opaque black paper on the back of the 120 film, and the film model and frame number (1 to 16) are printed on the backing paper;
• Emulsion Sticking/Offset:
• When the film is in a high-humidity and hot environment with a relative humidity exceeding 75% (such as the rainy season in the south of the Yangtze River, tropical rain forests or islands), the cellulose in the backing paper quickly absorbs water and expands;
• The printing chemical ink on the backing paper chemically adheres to the gelatin emulsion that is tightly attached to the other side;
• After being developed, a huge shadow of the backing paper number was printed on the film (such as a huge "KODAK 120" digital transfer mark), causing important pictures to be completely scrapped!

2. Cross-border travel and extreme climate ziplock bag packaging (Ziploc Vacuum Packing)

1. The iron law of freezing and warming of unopened film:

• When taking out the stored 120 film from the freezer (-18°C) or refrigerator (4°C), it is absolutely strictly prohibited to open the original aluminum foil plastic sealing bag immediately**!
• The original film must be left at room temperature to warm up:
• Take out from the refrigerator: let it stand for at least 2 hours;
• Take out of the freezer: let it stand for at least 6 hours;
• If the cold film comes into contact with hot and humid air at room temperature prematurely, the water vapor in the air will instantly condense into tiny dewdrops on the surface of the cold film, destroying the chemical structure of the film.

2. Quick sealing and dehydration after outdoor shooting (Travel Drying Kit):

• Carry thick, multi-layer sealed ziplock bags (Heavy-Duty Freezing Bags);
• Put 2 to 3 pieces of 120 film in each bag that have been shot and locked with seals;
  -Put in a small pack of Color Indication Silica Gel Desiccant (Silica Gel Packet);
• Insert a straw into the mouth of the bag to evacuate the air inside to a semi-vacuum state, and then quickly tighten the seal;
• The silica gel particles will continue to absorb the environmental moisture absorbed by the backing paper when shooting in the field, completely eliminating ink transfer caused by hot flashes on the way back.

3. The invisible killer of dry and cold environments in winter: Static Spark Marks

In dry and cold northern winters or highlands (relative humidity below 20%):

1. Principle of frictional electrification and discharge across sheets:

• The polyester (PET) or cellulose triacetate base of the film is an extremely excellent high-resistance insulator;
• When the film advance handle is quickly pulled in a low-temperature dry environment, or the film is quickly pulled out from a hidden bag, there will be severe friction between the film and the backing paper or the camera's film advance roller, instantly generating thousands of volts of static high voltage;
• Static electricity breaks through air breakdown discharge, and microscopic sparks burst out inside the cassette;

2. Pathological characteristics of electrostatic discharge films:

• Exposure marks similar to lightning-like, branch-like or black spider web-like will appear on the developed film;
• Many photographers mistakenly think that it is light leakage from the camera. In fact, the film itself is directly exposed by microscopic static sparks inside the camera body!

3. Static spark eradication operations:

• Slow down the film advance speed: In a cold and dry environment, the film advance wrench must be pulled extremely smoothly and evenly, and must not be pulled violently and continuously at high speed;
• Increase humidity: Before entering the indoor dark bag for rolling, gently spray a very fine water mist on the darkroom floor to increase the relative humidity of the environment to above 40% to help the natural release and dissipation of static charges.

4. Airport Customs Security Inspection Hand Inspection Communication Strategy

1. Penetrating destruction of 120 film by CT tomography:

• New airport carry-on baggage three-dimensional CT inspection machines (Smiths Detection / Analogic and other models) have extremely high ray energy;
• Even if it is a medium-format low-speed film with ISO 100, after just one CT scan, a strong green fog will appear in the dark part of the entire film, and the density of the film will completely collapse;

2. Customs inspection-free self-inspection package production:

• Before departure, peel all 120 films out of their cartons and plastic cases and pack them neatly into a completely transparent high-definition food-grade ziplock bag;
• Take the initiative to take out your backpack from your carry-on bag before the security check channel, hand it to the security inspection supervisor with both hands, and politely state in standard English: "Excuse me, these are professional unexposed photographic film rolls. Please could you perform a manual hand inspection? They will be destroyed by the X-ray/CT scanner."
• Never check it in! All films must be carried in the cabin with you at all times.

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