Platinum-Cured RTV for Food Molds, Not a Flask Pass

If you're specifying a custom RTV food mold, platinum-cured silicone means addition-cure polydimethylsiloxane: a platinum catalyst links vinyl and hydride groups, and no condensation byproduct has to leave the network for the cure to proceed. That's why food-contact mold rubber typically starts here — platinum RTV A/B poured against a master in a mold box, then post-cured.

It isn't a synonym for food-grade. FDA 21 CFR 177.2600 still extracts the finished cavity. LFGB/BfR XV still runs volatiles, simulants, and sensory. Platinum-cure doesn't make a pigment legal, doesn't replace post-cure, and doesn't mean FDA approved as a product registration. If the quote is LSR injection with a cold-runner, that's a molded *part*, not this mold.

Common mix-up: translucent, or “platinum-colored,” means addition-cure

A lot of RFQs treat a clear craft pour as platinum food-grade. In the shop that usually means tin-cure RTV (condensation, tin catalyst, a small molecule leaving the network) on a dirty SLA master, sticky from inhibition or leftover byproduct, filed under a platinum slogan.

Two shop chemistries get sold as “silicone molds.” Platinum addition-cure: A and B meet, hydrosilylation, little to no cure byproduct; inhibition is the process risk (tin, sulfur, some amines, some unpost-cured 3D-print resins). Tin-cure RTV: condensation, often moisture-participating, common for craft and many industrial masters, not the default food-contact path. Peroxide HCR is a third cure on millable gum for *parts* — unmix it on the RFQ.

What to ask when you're buying platinum RTV

• Is the kit platinum addition-cure A/B, named by grade, or “platinum or equivalent” (equivalent is how tin-cure sneaks in)?
• Mix ratio, vacuum degas, and a detail coat on fine logos — written on the traveler?
• How do they isolate the pour table from tin-cure so the catalyst doesn't die?
• Post-cure time scaled to the thickest wall, not a feel-dry-out-of-the-box skip?
• 21 CFR 177.2600 and/or LFGB/BfR XV on this SKU, separate from the chemistry line?

Why food-contact molds start on platinum — and still fail

177.2600 cares what leaves the finished article into water and n-hexane. BfR XV cares about volatiles and whether the article tastes like rubber. Addition-cure avoids tin catalyst and condensation byproduct as a starting load. A ventilated post-cure then drives off cyclics. That's “typical,” not “automatic.” Unlisted oils, dirty pigment, skipped bake, and release on the master still fail flasks.

LSR, platinum HCR, and platinum RTV can all be platinum addition-cure. They aren't interchangeable articles. A 177.2600 pass on an LSR spatula doesn't qualify a platinum RTV muffin tray. Process identity belongs in the report.

Inhibition is a manufacturing failure: tack, poor tear, a face that never dries. Food-contact shops isolate platinum lines for this reason, not only for paperwork. Post-cure is a different step. The part can be fully elastic and still fail volatiles or sensory. Don't invent a lab-only bake.

Worked example: sticky pour against an SLA master

A chocolatier wanted a 4-cavity 40 mm character, platinum RTV, keyed two-piece, about 300–600 dumps a month. The first pour stayed tacky against an unwashed SLA master.

That's inhibition, not a food-contact grade. Fix the master (full UV post-cure, wash, barrier coat), isolate gloves from tin-cure, and rerun. Don't ship a tacky food mold, and don't oil the tack. Once the network finishes, post-cure the thickest web, wash, and extract that article.

When platinum-cure talk is the wrong spec

Medical platinum LSR (ISO 10993, USP Class VI) isn't a bakeware ticket. Industrial platinum gasket compound isn't a chocolate cavity because it's platinum. Tin-cure can still be the right *resin* mold if you never touch food — don't force food-contact platinum into a soap job. A very large, dirty foundry pattern may tempt tin-cure for forgiveness; that still doesn't make it a 177.2600 article. Geometry and soil can override the brochure.

Related reading: what food-grade means, how we pour the mold, food-safe compounds, custom RTV molds.

What to send: two drawing lines, not one slogan

Copy this.

• Chemistry: platinum addition-cure RTV A/B (not tin-cure, not “or equivalent”)
• Process nouns: mix ratio, vacuum degas, pour against master, jacket, post-cure by max wall
• Test: 21 CFR 177.2600 food types and/or LFGB/BfR XV on the finished SKU
• Inhibition call-outs: 3D-printed masters, shared halls, sulfur gaskets
• Pigment code freeze; recast uses the same kit lot family

Send the drawing note and master photos. We'll unmix platinum-cure from “FDA food grade” slogans and tell you if the master will poison the catalyst.

We would not recommend "platinum or equivalent"

We would not recommend rebranding tin-cure by choosing a translucent pigment, or treating platinum industrial gasket compound as a chocolate cavity. We would not ship a tacky pour against an unwashed SLA master.

flowchart TD
  K[Kit on the RFQ] -->|platinum A/B 1:1 or 10:1| P[Addition-cure RTV]
  K -->|tin-cure| T[Condensation — wrong food-contact start]
  P --> I{Inhibition?}
  I -->|tacky vs SLA / tin / sulfur| F[Fix master and hall; scrap the face]
  I -->|network finished| C[Post-cure by wall]
  C --> E[177.2600 / BfR XV on this SKU]

Typical shop values: platinum RTV vs tin-cure

| Item | Typical shop value | | --- | --- | | Platinum mix | 1:1 or 10:1 by grade; vacuum degas | | Linear shrink | Platinum ~0.1–0.3%; tin keeps moving in storage | | Cavity Shore | 10A–20A + jacket for food dumps | | Inhibition tells | Tack, poor tear, face that never dries | | LSR / HCR contrast | Different articles; ~2–3% LSR shrink, ~1.5–2.5% HCR shrink on *parts* |

Caption these as typical shop values, not a lot we measured.

FAQ

Is platinum-cured silicone the same as food-grade silicone? Platinum addition-cure is the typical chemistry. Food-grade is the finished-article result under 21 CFR 177.2600 or LFGB/BfR XV. You can have platinum industrial parts that were never tested for food.

Why did my platinum RTV stay sticky against a 3D-printed master? Inhibition: some resins, tin, and sulfur poison the catalyst. That's a cure failure, not a food-contact grade. Fix the master and hall hygiene. Don't ship a tacky food mold.

Can I post-cure tin-cure RTV and call it platinum-equivalent? Different catalyst, different network, different byproduct story. Post-cure doesn't change tin-cure into addition-cure.

Does platinum-cure remove the need to wash the article? 177.2600 expects a thoroughly cleansed finished article. Trim dust and release still matter. Platinum is chemistry, not a wash.

Is “platinum-cured FDA approved” a valid combined claim? FDA doesn't approve the mold as a product registration. Name 177.2600 extraction of the article if you have the report, and name platinum-cure as the chemistry. Keep them as two facts.