Home / Grading Standards / Archival housing
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.
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
A strong sour or vinegary smell is the sign of vinegar syndrome: the acetate is hydrolysing and releasing acetic acid. Five things, in order.
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.
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.
| 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 |
| 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 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.
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.
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
| 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.
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.
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.
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.
This standard covers the housing of animation cels. The house conservation posture that applies to every category is at The record is the protection. Questions about a specific record or piece: 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). This page as Markdown.
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