Custom RTV Silicone Mold Texture Options on the Master

If you're buying texture on a custom RTV silicone mold, you're buying grain on the *master*: CNC-cut tooth, EDM (VDI 3400), chemical etch (MoldTech / MT 11000 and similar catalogs), laser, media, printed layer, or a cut-in logo. A JPEG from a catalog isn't a specification. Platinum RTV copies the pattern with little mercy. If the grain has an undercut, the dump will lock. If the grain is shallower than flash at the split, the texture vanishes at the parting.

Finish (polish of the master) is the neighboring topic. Texture is the patterned cousin. Don't write “light texture” on a drawing and expect two shops to match.

Steel LSR/HCR texture houses may still cut or etch a master for you. That doesn't turn this PO into a molded-*part* tool. If the quote lists cold-runners and heated cavities, you're looking at a different product line.

Four ways to put grain on a master

CNC tooth and engraved logos. Direct-cut grain, stitch, and lettering on aluminum or resin. Stroke width, depth, and draft belong on the logo drawing, not only in the AI file. Raised-on-dump versus recessed-on-dump is a mapping people flip: a pocket in the master becomes a raised rib on the silicone cavity, which becomes a pocket again in the gummy or chocolate.

EDM / VDI 3400. Spark erosion leaves an isotropic spark pattern when the master (or a metal pattern insert) can be burned. VDI numbers (12, 18, 24, 30, 36, and up) are the usual callout. Good for hiding flow in a cast resin and adding mild grip on bakeware. Not a leather, wood, or geometric brand grain.

Chemical texture (MoldTech, Yick Sang, and similar). Acid-etched patterns: leather, satin, geometric, custom brand grains. Depth and draft are in the catalog notes. The master has to be prepped (polish level before etch) or the grain will be muddy. This is the option when marketing wants a named look on soap, chocolate, or a consumer ice mold.

Laser, media, and printed layer. Laser writes local icons and patches that baths can't mask. Media and bead are fast dulling on a prototype master and hard to repeat lot-to-lot. SLA layer lines are an accidental texture: if you didn't want them, they're a finishing fail, not a grain option.

Grip, release, hygiene, and brand are different jobs. A bakeware grip wants depth that doesn't hold batter in a way that looks like flash. A chocolate bar may want a light satin so the bar releases, not a deep leather that traps cocoa butter. Food-contact and infant articles (FDA 21 CFR 177.2600, LFGB, CPSIA) don't forbid texture; they care about cleanability and compound. Deep undercut grains that trap residue are a hygiene argument, not a catalog argument.

Common mix-up: a photo as the texture spec

A lot of RFQs treat a JPEG or a “similar to MT-XXXX” note as enough. In the shop that usually means two lighting setups and two grains. Brand textures need a chip owned by the program. Keep it with the master, and use it at first casting and at incoming inspection.

Logo stroke that's narrower than the grain period will disappear. Combine logo and grain on a coupon before you commit a 12-cavity gummy tray. Don't accept “we'll texture after the first season if marketing likes the shape.” Adding grain to a finished master is a pattern change: polish, mask, etch or recut, then recast the RTV. Budget it as an engineering change.

If the article is two-shot resin or has a bonded insert, texture the silicone face and the substrate face as two notes. Primer and bond areas should stay untextured unless the bond spec allows a grain.

What to ask when you're buying

Send these with the artwork:

• Catalog code plus a physical chip, or a measured depth and process (VDI, laser, chemical, CNC)?
• Extra draft on the textured face, and grain depth in millimetres, not only a code?
• Keep-outs: sealing lips, logo pockets, splits — where does grain stop?
• Master material, and is there a barrier coat or plate that will fill the grain?
• Who keeps the chip with the master for recasts?
• First-casting photos under which lighting, including the last-to-fill region?

If two quotes don't name the same chip, you're not comparing the same look.

Draft, first casting, and a worked example

Texture is a forest of micro-undercuts. Thermoplastic rule-of-thumb tables are a start, then you prove them on RTV because the rubber stretches off the master and the dump has to later stretch out of the rubber. Stretch helps demold; tear on a thin letter doesn't.

Write minimum draft on the textured face (more draft for deeper grains), grain depth, keep-out zones, and the split blend. Texture that runs through a keyed split will chip and will show a bald stripe when the rubber wears. RTV won't copy a grain if the pour didn't wet the master (trapped air, incomplete degas) or if the grain is deeper than the wall of the dump can support. First-article photos should include the end-of-fill region of the *casting*, not only the pretty center.

Platinum holds the copy longer than tin-cure. Tin doesn't change the grain; it changes whether next season's recast still matches the chip.

Chemical, laser, and CNC houses need vector artwork, explicit “texture here / polish here” splits with radii, master material, and the plate/coat sequence. Plate-after-etch fills grain; etch-after-plate is a different process.

Worked example. A 10-cavity soap, 70 × 50 × 25 mm, needed a named leather grain on the show face and a clean split for a two-sided logo. The shop chemically etched the aluminum master to a catalog code plus a retained chip, left the logo pocket untextured, and poured platinum RTV in a keyed box with a resin jacket. First soaps matched the chip on the center and went slightly shallow at the split until pour head was raised. The chip stays with the master; a recast next year is useless without it.

When texture on the master is the wrong move

If the grain is only a JPEG, stop and buy a chip before anyone etches. Deep undercut leather on a food dump that has to be washed every shift is a hygiene problem, not a catalog win. LSR cavity etch with a cold-runner is a molded-*part* tool. A prototype print master can wear accidental layer lines as "texture"; don't freeze that as the brand grain. Geometry can override quantity: a 4-cavity soap with a named leather still needs more draft than a satin chocolate bar at 10,000 dumps.

Related: master surface finishes, engineering the split before the pour, custom RTV molds.

Texture pack to attach to the RFQ

• Catalog code plus a physical chip, or measured depth + process (CNC, VDI, laser, chemical)
• Extra draft on the textured face; grain depth in mm
• Keep-outs: lips, logo pockets, keyed splits
• Master material and any barrier coat / plate that will fill grain
• Who keeps the chip with the master for recasts

Send vector artwork, the chip (or a named MT/VDI code), and keep-out notes. We'll say whether the grain will copy, release, and still look like the chip after a recast.

We would not recommend a JPEG as the texture spec

We would not recommend etching from a phone photo, running grain through a keyed split, or freezing SLA layer lines as the brand grain. We would not put deep undercut leather on a food dump that is washed every shift and call it a catalog win. Extra draft belongs on the textured face; raising Shore A first will not hide a grain that is shallower than flash.

RUUIPON Mold Structure Decision: catalog code plus a physical chip, or measured depth + process. Keep-outs on lips, logo pockets, and splits. If the grain has a visible undercut the dump cannot peel, that face needs a split or a shallower grain — not a hope that rubber always comes out.

flowchart TD
  A[Texture job] --> B{Chip or measured depth?}
  B -->|JPEG only| C["Stop: buy a chip"]
  B -->|code + chip / VDI / CNC / laser| D["Keep-outs: lips, logo, keyed split"]
  D --> E{Grain undercut peelable in RTV?}
  E -->|yes + extra draft| F[Etch or cut master, then pour]
  E -->|no| G[Shallower grain or add a split]
  F --> H[First-casting photo vs chip, including last-to-fill]

Typical shop values

Caption these as typical shop values, not a named lot.

| Item | Typical shop value | | --- | --- | | Cavity Shore | 10A–20A platinum RTV, jacket behind it | | Mix | Platinum 1:1 or 10:1 by grade; vacuum degas until the foam collapses | | Platinum shrink after full cure | About 0.1–0.3% | | Mild dull default (not a law) | VDI 24-class spark or a light satin — pick by function | | Extra draft on deep leather | More than the untextured wall; catalog sheet is the start | | RTV skin wall | Often 8–15 mm; grain deeper than the dump wall will not copy well | | Loaded-tray edge sag | About 0.5–1.5 mm if the jacket is missing — grain looks “shallow” at the edge | | Outer-row gummy vs center if the tray sags | Edge often 3–6% heavy |

FAQ

Can I specify texture with a photo only? A photo is a wish. Use a catalog code plus a physical chip, or a measured depth and process (VDI, laser, chemical, CNC). Two shops lighting a JPEG differently will cut two grains. Keep the chip with the master.

How much extra draft does a deep leather grain need on an RTV master? More than the untextured wall, and more still if the grain has a visible undercut. The catalog sheet usually lists a recommended draft. Confirm on the production RTV because stretch helps, but thin walls still tear. Put the draft on the textured face, not only on the untextured CAD.

Will texture hide a bad pour gate or a bubble? It hides some of the shine. It doesn't fix a vent in the mold box or a degas miss. If the defect is a groove or a void, grain will sit on top of it. Fix the pour first, then use grain to make the rest of the article honest.

Does a barrier coat after chemical etch keep the same look? Coat fills and rounds the grain. If you need both inhibition protection on an SLA master and a named texture, define the sequence and approve a coated chip. A later recoat will need a texture restore plan.

Is VDI 24 a good default for all consumer RTV molds? It's a common mild dull, not a default. Grips, baking cavities, chocolate bars, and soap buttons want different depths and keep-outs. Pick by function, attach a chip, and keep sealing lips untextured.