Preparing your parts for coating.
PVD and DLC are thin, high-performance coatings that follow the condition of the surface beneath them. A little preparation up front is the single biggest factor in a clean, durable, great-looking result. Here's how to get the best coating possible — and the common part conditions to avoid.
Part condition requirement
For best results, parts must be received clean, dry, fully deburred, and free of oil, coolant, wax, polishing compound, rust, scale, oxidation, fingerprints, loose material, or unknown surface treatments. PVD and DLC coatings are thin and follow the condition of the base surface, relying on proper surface preparation for adhesion. Scratches, pits, burrs, stains, rust, handling damage, poor surface finish, or contamination may remain visible after coating and can reduce coating adhesion or performance.
Common part conditions that cause coating problems.
Each of these is preventable. Here's what causes it — and how to avoid it.
Oil, coolant, wax, polishing compound, or fingerprints
Even tiny amounts of cutting oil, hand oils, buffing or lapping compound, or wax interfere with the coating bonding to the base material — a leading cause of poor adhesion, peeling, blistering, staining, and inconsistent appearance.
- Send parts completely free of oil, coolant, grease, wax, polishing compound, and fingerprints.
- Wear clean gloves when handling finished parts.
- Avoid silicone-based sprays, anti-rust oils, WD-40-type products, or unknown protectants before coating.
- Do not package parts in oily paper, dirty foam, cardboard dust, or shop rags.
Rust, oxidation, scale, heat-treat discoloration, or passive oxide layers
PVD and DLC are thin films that bond to whatever surface they are deposited on. If that surface is rust, oxide, scale, or heat-treat residue, the coating bonds to the weak layer instead of the part. Stainless steels can also carry a passive chromium-oxide layer that may need proper surface activation before coating.
- Remove rust, scale, and heat-treat discoloration before sending parts.
- Avoid leaving parts exposed to humidity after cleaning.
- Use corrosion-preventive packaging only if approved by us first.
- For stainless, titanium, or highly passive materials, tell us the exact alloy and heat-treat condition.
Poor or inconsistent surface finish
A coating will not "fix" scratches, dents, chatter marks, burrs, pits, or weld marks — and because DLC is thin and conformal, it can actually highlight surface defects. Finish affects adhesion, appearance, friction, and durability.
- Finish the part to the desired final surface condition before coating.
- Remove scratches, burrs, sharp raised edges, and polishing drag marks.
- Keep the finish consistent from part to part.
- Decide up front whether the part should be polished, blasted, satin, matte, or left as-machined.
Burrs, sharp edges, thin corners, or fragile features
These thin, hard films can chip or flake at sharp burrs and feather edges, and coating thickness can build differently on edges, corners, holes, and complex geometry.
- Deburr parts completely before coating.
- Break razor-sharp edges unless the sharp edge is functionally required.
- Remove hanging burrs inside holes, slots, threads, and cross-holes.
- Tell us if cutting edges must stay sharp — such as knives, cutters, or medical blades.
Trapped fluids in holes, blind pockets, threads, porosity, or assemblies
Blind holes, threaded holes, porous materials, pressed assemblies, cracks, and tight seams can trap oils and cleaning fluids. In the vacuum chamber these outgas during coating, causing stains, pits, poor adhesion, or defects.
- Avoid sending assembled parts unless approved.
- Drain, clean, and dry blind holes, threaded holes, and cavities.
- Avoid porous castings, sintered parts, or impregnated parts unless reviewed first.
- A bake-out may be needed for porous or oil-soaked parts.
Plating, anodizing, nitriding, black oxide, passivation, or prior coatings
Existing surface treatments can cause adhesion problems if they are soft, oxidized, porous, contaminated, too thick, or incompatible with coating temperatures. Coating over an unknown treatment increases risk.
- Tell us about all prior treatments.
- Do not assume PVD/DLC can be applied over chrome, nickel, anodize, black oxide, phosphate, paint, powder coat, or another PVD coating.
- Strip old coatings or plating when required.
- Provide material certs or process history for critical parts.
Material or heat-treat condition not suited to the coating temperature
Many PVD and DLC processes run at elevated temperatures. Substrates that are too soft, improperly heat treated, low-temperature tempered, soldered, brazed, epoxied, or dimensionally unstable may soften, distort, discolor, or lose performance.
- Provide exact material, hardness, and heat-treat condition.
- Verify the part can tolerate the coating temperature — or ask about our low-temperature Black Widow DLC (200 °C).
- Notify us about solder, braze, adhesive, magnets, springs, press fits, or heat-sensitive inserts.
- For tooling, make sure substrate hardness supports the coating.
Poor packaging and shipping damage
Parts can arrive scratched, dinged, contaminated, mixed together, or rusted. PVD/DLC coatings are cosmetic and functional, but they cannot hide shipping damage.
- Package parts individually or in clean trays.
- Prevent metal-to-metal contact.
- Use clean plastic bags, clean foam, or dedicated part packaging.
- Label parts clearly by material, coating, quantity, and masking requirements.
Incorrect or unclear masking instructions
Coating is line-of-sight or semi-line-of-sight depending on the process, so masking must be planned carefully. Unclear instructions can leave coating where it is not wanted, or missing where it is needed.
- Provide clear drawings showing coated and uncoated areas.
- Mark critical surfaces, threads, bores, sealing faces, electrical contacts, and datum surfaces.
- Confirm whether masking marks, rack marks, or contact points are acceptable.
- Identify cosmetic "A" surfaces.
Dimensional tolerance issues
PVD/DLC coatings are thin, but they still add thickness. Tight bores, threads, bearing fits, seals, gauges, and precision mating features can be affected.
- Tell us which dimensions are critical.
- Confirm coating thickness before manufacturing final dimensions.
- Allow for coating buildup where necessary.
- Mask tight-tolerance features if coating cannot be tolerated.
Pre-shipment prep checklist.
Run through this before sending parts for the cleanest, most consistent results.
- Finish machine, polish, blast, grind, or deburr parts to the final required condition.
- Remove burrs, sharp hanging edges, loose material, and chips.
- Clean off all oil, coolant, wax, polishing compound, rust inhibitor, fingerprints, and shop residue.
- Dry parts completely — especially holes, pockets, threads, and assemblies.
- Handle with clean gloves after final cleaning.
- Package parts so they cannot rub, scratch, rust, or collect dust.
- Provide material, hardness, heat-treat condition, prior surface treatments, and coating requirement.
- Provide drawings for masking, critical surfaces, cosmetic areas, and tight tolerances.
- Identify parts previously coated, plated, welded, brazed, soldered, glued, passivated, anodized, nitrided, or chemically treated.
- Ask us before sending unusual materials, assemblies, porous parts, or heat-sensitive parts.
Not sure about a material, assembly, porous part, or heat-sensitive part? Ask us before you ship — we're glad to advise.
Coating risk notice
Crystallume PVD is not responsible for coating defects, cosmetic variation, adhesion issues, discoloration, peeling, staining, dimensional interference, or performance issues caused by customer-supplied part conditions — including but not limited to contamination, oil, coolant, polishing compound, rust, oxidation, scale, burrs, sharp edges, poor surface finish, prior coatings, plating, heat-treat residue, passivation, trapped fluids, porous materials, assemblies, unknown alloys, or inadequate packaging. Parts submitted with non-standard or unknown surface conditions may be processed "as is" at the customer's risk unless special preparation, testing, or inspection is requested and approved in advance. See our Terms & Conditions for full details.
Questions about prepping your parts?
Tell us your part, material, and application — we'll confirm the right prep, masking, and coating before anything ships.