Structural Risk from Binder Storage
In the Cel Nexus framework, structural risk (Lstruct) is everything that can physically deform a cel even if the chemistry stayed perfectly stable. Binders introduce two distinct structural risks:
- Compression risk (Lstruct,comp) – vertical stacks of pages pressing down on raised paint, texture, or stuck areas. This is the focus of this article.
- Bending / cycling risk (Lstruct,bend) – pages stored vertically that sag, bow, or creep over time, especially when relative humidity cycles. This will be explored in a separate blog and summarized in the framework appendix.
Here we quantify the first of these: localized contact pressure in horizontal binders. We take real weights from a loaded 11×14 Itoya, convert them into contact pressures on a raised paint patch, and map the results into green / yellow / red bands that tie directly into Lstruct,comp in the preservation framework.
Model Assumptions
- 20 pages in an 11×14 Itoya binder.
- Half of the shell mass (0.284 kg) treated as a conservative “lid” on the stack.
- Page masses from weighed samples: 119.5 g, 84.5 g, 58.5 g for Configs A–C.
- Static loads (no drops/impacts) at room temperature.
- Raised-paint contact patch ≈ 5 cm² (worst-case ridge geometry).
1. Localized Contact Pressure Is the Real Risk
Paint transfer and imprinting happen where raised features actually touch a neighboring surface. Collectors often hear vague guidance like “don’t stack too many cels” or “keep binder stacks small,” but these rules of thumb have no first-principles derivation. What matters is pressure at the contact patch, not the raw stack count.
Measured Itoya Example (20 Loaded Pages)
Instead of a toy example, we can use real weights from a loaded Itoya binder (11×14″ pages in polypropylene sleeves). We’ll look at three realistic configurations:
-
Config A – Full stack (heaviest):
Itoya PolyGlass sleeve (38 g) + Itoya black insert sheet (26 g) + backing board (35 g) + cel in its own sleeve (average 20.5 g) →m_page ≈ 119.5 g. -
Config B – Full stack, no backing board:
Itoya PolyGlass sleeve (38 g) + Itoya black insert sheet (26 g) + cel in its own sleeve (20.5 g) →m_page ≈ 84.5 g. -
Config C – Cel + Itoya PolyGlass sleeve:
Itoya PolyGlass sleeve (38 g) + cel in its own sleeve (20.5 g) →m_page ≈ 58.5 g.
The binder shell + rings are ≈ 568 g. For a conservative worst case, we assume half of that (0.284 kg) sits directly on top of the page stack, even though in reality a ring binder often carries some of that weight in the spine and hardware. Binder geometry varies, so we intentionally assume a heavy cover to avoid underestimating compression risk.
In the heaviest full-stack configuration (Config A), a 20-page horizontal binder holds ≈ 2.4 kg of pages alone. With half of the shell weight added on top, the bottom page sees about 2.55 kg of load above it. Lighter configurations (Configs B and C) reduce that by a meaningful amount.
Load Down the Stack – Comparing Configurations
For each page position, the table below shows the total mass above that page (pages + 1/2 shell) for the three configurations:
- Config A – Full stack: 119.5 g / page
- Config B – Full stack, no backing board: 84.5 g / page
- Config C – Cel + Itoya PolyGlass sleeve: 58.5 g / page
| Page position (from top) |
Config A (kg, pages + ½ shell) |
Config B (kg, pages + ½ shell) |
Config C (kg, pages + ½ shell) |
|---|---|---|---|
| 1 | 0.284 | 0.284 | 0.284 |
| 2 | 0.403 | 0.368 | 0.342 |
| 3 | 0.523 | 0.453 | 0.401 |
| 4 | 0.642 | 0.537 | 0.460 |
| 5 | 0.762 | 0.622 | 0.518 |
| 6 | 0.881 | 0.707 | 0.577 |
| 7 | 1.001 | 0.791 | 0.635 |
| 8 | 1.120 | 0.876 | 0.694 |
| 9 | 1.240 | 0.960 | 0.752 |
| 10 | 1.359 | 1.045 | 0.811 |
| 11 | 1.479 | 1.129 | 0.869 |
| 12 | 1.598 | 1.214 | 0.928 |
| 13 | 1.718 | 1.298 | 0.986 |
| 14 | 1.837 | 1.383 | 1.045 |
| 15 | 1.957 | 1.467 | 1.103 |
| 16 | 2.076 | 1.552 | 1.162 |
| 17 | 2.196 | 1.636 | 1.220 |
| 18 | 2.315 | 1.721 | 1.279 |
| 19 | 2.435 | 1.805 | 1.337 |
| 20 (bottom) | 2.554 | 1.890 | 1.396 |
The bottom cel in a fully loaded 20-page binder sees anywhere from ~1.4 kg (Config C) up to ~2.6 kg (Config A) pressing down on any raised paint.
So What Does This Mean?
A load of 1.4–2.6 kg on the bottom cel may not sound dramatic, but what matters is how that load is delivered. That entire mass is supported by a cel whose raised paint, texture, or stuck areas may only be touching the page above over a contact patch of 1–5 cm².
When a multi-kilogram stack rests on a very small area, the resulting local pressure can become large enough to:
- flatten or bruise raised paint,
- transfer texture or blocking patterns,
- cause “ghost” imprints of stuck areas, especially in VS-active cels,
- slowly deform the cel stack over multi-year dwell.
This is why we convert mass → pressure. The raw kilograms don’t tell you the risk; the psi at the raised feature does. Once we express each configuration in terms of local pressure, we can evaluate:
- Which binder setups stay in the safe zone for long-term storage,
- Which ones creep into the caution or risk zones, and
- Which pages (top, middle, bottom) need mitigation or should not hold valuable cels.
The next section translates these bottom-page loads into pressure tiers that directly map to Lstruct,comp in the preservation framework.
Pressure Tiers and Example Loads
To make the pressure bands intuitive, the table below links each tier
to a real physical load in a binder. All examples use
P = F/A with F = m·g
(g ≈ 9.81 m/s²).
| Tier | Pressure band (psi) | What it means | Example load |
|---|---|---|---|
| Green – Low | ≲ 2 psi | Comparable to light stacks of paper or a very gentle touch. For stable cels at good T/RH, this produces negligible mechanical deformation even over many years of storage. | ~0.3 kg of paper over a 10×10 cm area (100 cm²) → ~0.04 psi. |
| Yellow – Caution | ~2–5 psi | Comparable to the load experienced by a cel when the binder shell plus ~7 fully loaded pages sit above it — about 1.0–1.1 kg (≈ 2.2 lb). This is not instant failure, but it is a time-dependent risk band: safe for handling and short-term dwell, yet capable of contributing to blocking, texture transfer, or raised-paint creep over months to years, especially if the cel is chemically unstable. | 1.0 kg on a 5 cm² raised-paint patch → ≈ 3.0 psi. |
| Red – Manage or Mitigate | > 5 psi | Comparable to a firm fingertip press on a small area. Not instant failure, but undesirable as a long-term resting load. A cel in the red band should be moved, unloaded, or transferred to vertical storage, especially if VS is active. | 1.0 kg load on 2 cm² → ~7.1 psi. |
How Were These Pressure Bands Chosen?
These bands are not magic numbers; they are conservative ranges chosen to be protective over years of storage, not minutes of handling. Deformation depends on three things:
- How hard you press – the local pressure P = F / A.
- How long the load stays – hours vs. multi-year dwell in a binder.
- How small the contact patch is – sharp ridges and islands concentrate load much more than broad flat paint.
Because there is almost no published data specific to animation cels, the bands here are anchored to three pieces of information:
- Behavior of textured artist paints. Conservation data for textured acrylic and vinyl paints on flexible substrates shows that long-term loads of roughly 2–5 psi on small contact areas can slowly flatten raised features, especially when the material is already chemically weakened.
- Real binder loads. A 20-page 11×14 Itoya can easily put 1–7 psi on the bottom cel depending on configuration. The bands are chosen so that a typical loaded binder spans all three regions.
- Conservative geometry. We assume a raised-paint contact patch of about 5 cm². Some cels are painted very flat and broad; in those cases the effective contact area is much larger and the local pressure drops toward zero. Others have thick line work, ridges, or small islands of paint that really do touch over only a few square centimeters. This framework is deliberately tuned to that worst-case geometry – the ridges and islands, because that is where damage starts. If your cel is perfectly flat, your true risk is lower than these tables show; but we engineer for the ridges to stay on the safe side.
In other words, the green / yellow / red ranges are not instant-failure thresholds. They are comfort zones:
- Green (≲ 2 psi) – negligible deformation for stable cels at good T/RH.
- Yellow (~2–5 psi) – cumulative risk band; years of dwell can contribute to blocking or texture transfer, especially if VS is active.
- Red (> 5 psi) – firm fingertip-press territory; acceptable for handling, but undesirable as a long-term resting load on raised paint.
How Big Is the Contact Patch? (Technical Details)
To translate load into pressure, we need an estimate of the contact area where raised paint actually touches the page above. Cels rarely press perfectly "flat on flat" — contact happens through ridges and islands of thicker paint. A few reasonable assumptions:
- Typical linework and ridges are 0.5–1.5 mm wide and several centimeters long.
- Several ridges bear load simultaneously under a stack.
- This gives an effective bearing area of roughly 1 cm × 5 cm = 5 cm².
For the pressure tables below, we use a conservative 5 cm² contact patch. A larger patch (like 10 cm²) would produce lower pressures — meaning our numbers err on the safe side.
To convert the masses above into the pressure values shown in the next table, we assume a conservative 5 cm² raised-paint contact patch (0.0005 m²). This represents a small but realistic area of thick paint that may bear most of the load when a cel is compressed inside a sleeve. Pressure is computed using P = F / A, with F = m·g (g ≈ 9.81 m/s²).
As an example, consider Config A at page position 7 in the
table above, which carries 1.001 kg of mass. The force is
F = 1.001 × 9.81 ≈ 9.82 N. Applying this force to a
5 cm² (0.0005 m²) contact area gives
P = 9.82 / 0.0005 ≈ 19,640 Pa, which converts to
≈ 2.8 psi. This value appears directly in the pressure table
below. Lighter configurations (B and C) follow the same calculation but with
smaller masses, resulting in lower pressures.
With that conversion in mind, the next table color-codes each page position according to the pressure tiers defined earlier: green (low), yellow (caution), and red (manage or mitigate). This makes it easy to see how different configurations distribute mechanical load through the binder stack.
The colored table below applies these bands to each page position and configuration.
| Page position (from top) |
Config A (psi) |
Config B (psi) |
Config C (psi) |
|---|---|---|---|
| 1 | 0.8 | 0.8 | 0.8 |
| 2 | 1.1 | 1.0 | 1.0 |
| 3 | 1.5 | 1.3 | 1.1 |
| 4 | 1.8 | 1.5 | 1.3 |
| 5 | 2.2 | 1.8 | 1.5 |
| 6 | 2.5 | 2.0 | 1.6 |
| 7 | 2.8 | 2.3 | 1.8 |
| 8 | 3.2 | 2.5 | 2.0 |
| 9 | 3.5 | 2.7 | 2.1 |
| 10 | 3.9 | 3.0 | 2.3 |
| 11 | 4.2 | 3.2 | 2.5 |
| 12 | 4.6 | 3.5 | 2.6 |
| 13 | 4.9 | 3.7 | 2.8 |
| 14 | 5.2 | 3.9 | 3.0 |
| 15 | 5.6 | 4.2 | 3.1 |
| 16 | 5.9 | 4.4 | 3.3 |
| 17 | 6.2 | 4.7 | 3.5 |
| 18 | 6.6 | 4.9 | 3.6 |
| 19 | 6.9 | 5.1 | 3.8 |
| 20 (bottom) | 7.3 | 5.4 | 4.0 |
These pressures are calculated for a loaded 11×14 sized Itoya binder. Smaller binders generally reduce the total mass above each cel; larger binders and heavier shells increase it. The color bands (Green / Yellow / Red) still apply – only the exact numbers shift as your binder geometry changes.
2. Interpreting the Data: The "Backing Board Paradox"
The results highlight a counter-intuitive trade-off in preservation planning. We often add backing boards (Config A) to provide rigidity and prevent bending. However, in a horizontal stack, those boards add significant mass.
Config A (Full Rigidity) pushes the bottom third of the binder into the Red Zone (>5 psi). The rigidity meant to protect the cel from bending is actively contributing to compression damage on the pages below it.
Config C (Minimalist) keeps almost the entire binder in the Green or low-Yellow zones, but it offers the least protection against handling accidents or bending if the binder is ever stood upright.
The top 25% of any binder is the "Safe Zone." regardless of configuration, the top 4–5 pages rarely exceed 2.0 psi. If you have extremely high-value or fragile cels (thick paint, heavy line work), they belong at the front of the book, not the back.
3. Mapping Risk to Mitigation
Using the framework, we don't just identify risk; we apply mitigations to move cels back into acceptable safety margins. Here is how to handle your collection based on the pressure tiers.
For the Green Zone (< 2 psi)
Status: Negligible Risk
- Action: Standard monitoring (chemical only).
- Context: As long as Temperature and Humidity are controlled, compression risk here is effectively zero. No special rotation or handling is required.
For the Yellow Zone (2–5 psi)
Status: Manageable Risk (Lstruct active)
The load is high enough that years of dwell time could cause faint texture transfer or paint flattening.
- Mitigation A (Rotation): "Shuffle" the binder once a year. Move bottom pages to the top to relieve pressure dwell time.
- Mitigation B (Interleaving): Place a sheet of smooth MicroChamber paper over the cel surface. This distributes point-loads from the sleeve above and prevents direct plastic-on-paint contact, reducing the chance of adhesion (blocking).
- Mitigation C (Load Reduction): If using backing boards (Config A), consider removing them for the bottom half of the stack to shift the weight profile closer to Config B.
For the Red Zone (> 5 psi)
Status: Avoidance Required
Pressures above 5 psi can cause permanent deformation to acrylic paint within 12–24 months and are not recommended for indefinite storage.
- Avoidance A (Binder Splitting): Do not fill 11x14 binders to capacity. Instead of one 20-page binder, use two 10-page binders. This keeps all pages in the Green/Low-Yellow tiers.
- Avoidance B (Vertical Transfer): Move these cels to vertical storage (see below).
4. The Secondary Factor: Gas Diffusion
While this article focuses on mechanical pressure, we must briefly address chemical outgassing (Lchem,emit).
Horizontal stacking creates a "tight seal" effect. Gravity presses the pages together, reducing airflow between sleeves. If a cel in the middle of a stack begins to outgas (Vinegar Syndrome), the acetic acid is trapped in the immediate vicinity, creating a high-concentration micro-environment that accelerates degradation of neighbors.
Vertical storage inherently leaves small air gaps between pages (unless packed too tightly). This allows for natural diffusion, letting acidic off-gassing escape the immediate sleeve area more easily.
Conclusion: Which Method Wins?
There is no single "correct" way to store a cel, but there is a clear engineering hierarchy based on risk tolerance.
1. Vertical Storage (The Gold Standard)
Best for: Large collections, chemically active cels.
Vertical storage (in box/bin systems with rigid boards) eliminates
Lstruct,comp entirely. The only risk is bending,
which is easily mitigated by using stiff backing boards and ensuring the bin
isn't too loose. It also offers better airflow for chemical stability.
2. Horizontal Storage (The Calculated Risk)
Best for: Display binders, small collections.
Horizontal binders are acceptable IF you manage the weight.
If you store cels horizontally, limit stacks to 10–12 pages (splitting one full binder into two). If you must fill a binder to 20 pages, place your most valuable cels in the top 5 slots.
By understanding the physics of contact pressure, we move away from superstition ("binders are bad") toward calculated risk management ("binders are tools with load limits").