# Archival Housing of Animation Cels What a cel is sent home in, what it is not sent home in, and why. A clear polypropylene sleeve, open along one full edge, so the acid a cel produces can leave it. Published for owners, conservators and anyone who wants to check our reasoning. Category: Animation cels · Developed by Rinkya Authentic · Published September 2026 ## The standard, in one paragraph RKJ animation cels are housed in clear, conservation-grade polypropylene sleeves that remain open along one full edge to permit exchange of volatile degradation products. Polypropylene is recognised by the Library of Congress,¹ the National Archives and Records Administration,² and the Canadian Conservation Institute³ as a chemically stable material appropriate for preservation enclosures, and CCI recommends it for long-term encapsulation. Loose cel layers are separated using 2-mil polyethylene interleaving, consistent with documented storage practice at the Walt Disney Animation Research Library.⁴ ## The four tenets Nothing sealed. One full edge stays open. A closed enclosure holds the acid against the piece. No paper against paint. Cel paint adheres to fibrous surfaces. What is right for a negative is wrong for a cel. Clarity outside, function inside. The owner sees the piece through the sleeve. The interleaving is not a viewing surface. Nothing implied. The sleeve does not depend on a reading. The open edge lets the acid leave whether or not anyone measures it. A cel already in vinegar syndrome is the one case we do not sleeve. ## If a cel is already degrading, act on this first A strong sour or vinegary smell is the sign of vinegar syndrome: the acetate is hydrolysing and releasing acetic acid. Five things, in order. - **Isolate it from other acetate.** NARA directs that deteriorating acetate be stored separately to prevent damage to other holdings,² and the Getty and Disney study likewise recommends identifying and isolating affected cels to prevent accelerating hydrolysis in lower-risk cels stored nearby.⁴ Acid emitted by one piece is a source of decay for its neighbours. - **Increase air exchange. Do not reach for a tighter enclosure.** The instinct to seal a deteriorating piece away concentrates exactly what needs to leave.⁷ - **Cool and dry, if available.** Emission falls with temperature and humidity.⁷ - **Never separate fused layers.** Layers stuck to each other, or to a background, are one object. Separation is a conservator's treatment decision, and attempts routinely remove paint.⁴ - **Refer when the signs are advanced.** Specialist treatment is available through accredited film and paper conservation laboratories. For animation art specifically we refer to [Cel Oasis](https://celoasis.com), Osaka, who conserve and frame animation art and whose frames are deliberately left unsealed so the cel can breathe. **What happens when one reaches us.** A cel with a strong vinegar smell at examination is examined in full and its record is published, but it is not sleeved and no seal is applied until it has been treated: the sleeve is the one thing we would be adding, and the piece needs air, not an enclosure. It is kept apart from other acetate while it is with us. Treatment is a conservator's work; we refer to Cel Oasis, Osaka. Once the piece has been treated and examined again, it is sleeved and sealed, and its record is revised to say so. ## 1. The construction ### Single stable cel - Cel - Clear polypropylene sleeve, open along one full edge ### Multiple loose cel layers - Cel - 2 mil polyethylene interleaf - Cel - 2 mil polyethylene interleaf - Cel - All of it inside one clear polypropylene sleeve, open along one full edge ### Layers fused to each other, or a cel fused to its background - The assembly, left intact and untouched - Clear polypropylene sleeve, open along one full edge ### A cel with vinegar syndrome - Not sleeved until it has been treated (see the section above) The polypropylene is the viewing surface and the physical protection. The polyethylene appears only between layers, where nobody looks at it and where the Disney and Getty citation applies directly.⁴ Nothing in the stack is sealed, adhered or irreversible. ## 2. Material specification ### Outer sleeve | Requirement | Specification | | Polymer | Clear, uncoated, unplasticised polypropylene | | Closure | One full edge open. No adhesive, no flap, no heat seal, no zip | | Additives | None. No fillers, coatings, UV absorbers, slip agents or antistatic treatment | | Visual test | No surface haze. Haze indicates a coating or heavy plasticiser¹ | | Certification | Meeting ISO 18902, and passing the Photographic Activity Test, ISO 18916¹˒⁵ | | Never | PVC or vinyl | ### Interleaving, loose layers only | Requirement | Specification | | Polymer | Virgin polyethylene, uncoated, no additives | | Thickness | 2 mil⁴ | | Use | Between cel layers only. Never as the outer enclosure, never against a background | **Why not paper.** Standard guidance for acetate *negatives* is an alkaline-buffered paper enclosure, because plastic can hold decomposition products against the film. It must not be carried across to cels. A cel is painted, cel paint adheres to fibrous surfaces, and interleaving paper is documented sticking to the back of cel paint, with removal damaging the cel.⁴ Same base material, opposite enclosure, because one of them is painted. ### The seal The RKJ seal is a holographic label applied to the exterior of the sleeve. It never contacts the piece, and its adhesive never touches anything but the polypropylene. Because the housing remains open along one full edge it is not a closed system, so no emission from the seal is concentrated against the cel. The face stock is a metallised polyester film, which is one of the three plastics accepted for preservation enclosures.¹ The adhesive chemistry is not yet specified here, and no archival or Photographic Activity Test claim is made for the seal until its construction has been confirmed by the manufacturer. **Before you rehouse a sealed piece, tell us.** The seal is on the sleeve, and the sleeve is a consumable. This standard asks owners to replace a sleeve that has clouded, slumped or gone brittle, and doing that disturbs the seal. Contact us before you move the piece, not after. Housing a piece correctly must never cost an owner their record. **Why not Mylar, even though it is clearer.** Polyester is the clearest option and is otherwise an accepted preservation plastic. It is excluded here on one measured ground: acetic acid either does not diffuse through PET at all, or diffuses too slowly to measure, because the acetic acid molecule is larger than water.⁶ A cel is an object we deliberately do not want isolated from the air, so the clearest material is the wrong one. ## 3. Why one edge is left open The escape route is the open edge, not diffusion through the sleeve wall. That distinction matters, because polypropylene's permeability varies with crystallinity, orientation and additives, and engineered high-transmission PP films exist. "Polypropylene lets the acid out" is not a defensible blanket claim, so this standard does not make it. The open edge, by contrast, is measured. In encapsulation testing, keeping one edge open produced a drying rate **four times faster** than sealing all four sides.⁶ The principle also has direct institutional precedent on this exact material. NARA specifies archival polypropylene containers for motion-picture acetate and states that cans allowing venting around the lid are preferred, to prevent a concentration of acetic gases inside that accelerates deterioration.² Polypropylene plus deliberate ventilation is an established combination for cellulose acetate, not an invention of ours. ## 4. Where the owner keeps it Rinkya supplies the sleeve and nothing further. What it goes into is the owner's, and this is stated by material, never by brand: **a conservation-grade polyethylene, polypropylene or polyester portfolio or an archival box. Never PVC.** Common collector portfolios in polypropylene satisfy this, which is deliberate: the housing is designed to go where cels are actually kept rather than to be removed on arrival. | Requirement | Specification | | Box, where used | Uncoated archival paperboard. Not surface-coated or laminated⁷ | | Volume | A larger internal volume is preferred to a tight fit; dilution lowers the equilibrium concentration⁷ | | Orientation | Flat, on a board cut larger than the piece. Never upright, never under weight | | Scavengers | Not packed against the object. A sorbent used in mounted cels was shown to remove plasticiser from them⁴ | A 2025 study modelling equilibrium acetic acid concentrations inside four enclosure types found surface-coated archival boxes held the highest concentrations, from their low air exchange rates and deposition velocities. Uncoated paperboard, being permeable and porous, reached lower concentrations, and display cases lower still, because a larger internal volume dilutes what is emitted.⁷ ## 5. Conditions | Parameter | Target | Source | | Temperature | 62 to 65 °F (17 to 18 °C) | Disney ARL vaults⁴ | | Relative humidity | 50% ±2% | Disney ARL vaults⁴ | | Humidity ceiling for plastic | Avoid plastic enclosures where prolonged storage above 80% RH is likely; surfaces adhere | Library of Congress¹ | | Acetic acid in air, acid-sensitive | Below 10 µg·m⁻³ | Literature cited in⁷ | | Acetic acid in air, general collection | 100 to 700 µg·m⁻³ | Literature cited in⁷ | Good conditions slow the process; they do not stop it. Degrading acetate emits acetic acid at significant rates even at 20 °C and 30% RH, the conditions prescribed for its storage.⁷ Emission from thin acetate is governed by surface evaporation rather than internal diffusion,⁷ and a cel is thin, which is why air movement at its surface matters here in a way it would not for a thick object. ## 6. Monitoring Withdrawn in this edition. Earlier editions of this standard specified an acid-detecting strip protocol and a level scale for cels. Both are withdrawn. The strip was developed for motion-picture film, a mass of base in a closed can. A single painted cel is a different object, and one reading from it describes the air in the test enclosure on that day, not the piece. A baseline for a cel takes a series of readings over time, and a baseline is a treatment tool: it belongs with the conservator treating the piece, not on a condition record. The chemistry of paint on acetate is thinly studied, because the acetate literature was written for film. Vinegar syndrome is therefore recorded as what the examination observes, under the grading standard for the category, and no stage is assigned to it. Our housing never depended on a reading. The open edge lets the acid leave whether or not anyone measures it. ## 7. What an owner receives A cel in a clear polypropylene sleeve, open along one full edge. That is the housing, and it is deliberately the whole of it: it goes straight into whatever the owner already keeps their collection in. Multi-layer setups arrive with 2 mil polyethylene between the layers. Fused assemblies arrive intact, in a sleeve, with a note that they are not to be separated. The one exception is a cel with vinegar syndrome, which goes back without a sleeve until it has been treated. Kept flat, cool, dry and not sealed into anything, a cel housed this way is doing as well as the material allows. ## References Compiled from the published literature cited below. Each source was checked against its original publication in September 2026. Where a commonly repeated claim could not be verified in the source it was attributed to, it was removed rather than repeated. - 1. Library of Congress, Care, Handling and Storage of Photographs. Suitable plastic enclosures are uncoated polyester, polyethylene and polypropylene; avoid plastics with fillers, coatings or UV absorbers, and any showing surface haze; avoid plastic where storage above 80% RH is likely; photo-safe requires ISO 18902 including the PAT, ISO 18916. - 2. National Archives and Records Administration, guidance on the storage of motion picture film. Archival polypropylene containers; cans that vent around the lid preferred, to prevent concentration of acetic gases; deteriorating acetate isolated from other holdings. - 3. Canadian Conservation Institute, Technical Bulletin 32, Products Used in Preventive Conservation. Polypropylene: stable, does not become brittle with age, recommended for long-term encapsulation. Cellulose acetate not recommended for long-term storage. - 4. McCormick, K., Schilling, M. R., Truffa Giachet, M., Mazurek, J., Khanjian, H., & Learner, T. (2014). Animation Cels: Conservation and Storage Issues. AIC Objects Specialty Group Postprints 21, 251-261. A Getty Conservation Institute and Walt Disney Animation Research Library collaboration. [resources.culturalheritage.org](https://resources.culturalheritage.org/wp-content/uploads/sites/8/2015/03/osg021-11.pdf) - 5. ISO 18916, Imaging materials: Photographic activity test for enclosure materials. Developed by the Image Permanence Institute, Rochester Institute of Technology. Enclosure requirements are covered by ISO 18902. - 6. The Permeability of PET by Formic and Acetic Acid Vapors. Studies in Conservation 68(4). doi:10.1080/00393630.2021.2011685. Acetic acid did not measurably permeate PET; one open edge gave a drying rate four times that of a four-side seal. [doi.org/10.1080/00393630.2021.2011685](https://doi.org/10.1080/00393630.2021.2011685) - 7. Novak, M., Grau-Bové, J., Rijavec, T., Kraševec, I., Kralj-Cigić, I., De Stefani, C., Checkley-Scott, C., & Strlič, M. (2025). A quantitative study of acetic acid emissions from historical cellulose acetate at room conditions. npj Heritage Science 13, 22. doi:10.1038/s40494-025-01551-y [doi.org/10.1038/s40494-025-01551-y](https://doi.org/10.1038/s40494-025-01551-y) [The record is the protection →](https://www.rinkya.com/authentic/grading/conservation) [Get a piece authenticated →](https://www.rinkya.com/authentic/japancollectibles#apply) [← All grading standards](https://www.rinkya.com/authentic/grading) This standard covers the housing of animation cels. The house conservation posture that applies to every category is at [The record is the protection](https://www.rinkya.com/authentic/grading/conservation). Questions about a specific record or piece: [authentic@rinkya.com](mailto:authentic@rinkya.com). Cite as: Rinkya Authentic, "Archival Housing Standard for Animation Cels" (version 2026.09-4, October 2026), https://www.rinkya.com/authentic/grading/housing Free to quote and share with attribution to Rinkya Authentic and a link to this page. Not for commercial republication or derivative standards ([CC BY-NC-ND 4.0](https://creativecommons.org/licenses/by-nc-nd/4.0/)). [This page as Markdown](https://www.rinkya.com/authentic/grading/housing.md).