--- title: "Rack Marks on Anodised Cookware — Where They Land and How to Move Them | Saravana Consultancy" description: >- Rack marks are the largest source of cosmetic rejection on Indian hollowware lines. Where the contact point should sit on a kadai or tawa, why titanium not aluminium, and how to diagnose burns, thin coating and partial anodising. canonical: "https://www.saravanaconsultancy.in/blog/rack-marks-anodised-cookware" source_url: html: "https://www.saravanaconsultancy.in/blog/rack-marks-anodised-cookware" md: "https://www.saravanaconsultancy.in/blog/rack-marks-anodised-cookware.md" last_modified: 2026-08-20 --- # Rack marks on anodised cookware — where they land and how to move them Balasubramanian Iyer · August 2026 Every anodised part carries a mark where the current entered it. On an architectural profile that contact point sits inside a glazing pocket and no one ever sees it. On a kadai or a tawa there is nowhere to hide, which is why rack marks are the single largest source of cosmetic rejection on Indian hollowware lines — and why they are almost always designed in rather than caused on the shop floor. ## Why the mark exists at all Anodising is an electrochemical process. Current has to pass from the rack into the part, through the electrolyte, and back to the cathode. Wherever the jig physically touches the workpiece, that contact area is shielded: no electrolyte reaches it, so no oxide grows there. What is left after the tank is a small patch of bare or thinly coated aluminium. The patch cannot be avoided. It can only be **moved, minimised, or hidden**. Anyone selling you a jig that leaves no mark is either using a sacrificial contact that will itself become a defect, or has not run production yet. ### Why hollowware is worse than profiles Three things compound on a vessel: - **Every surface is visible.** A pan is handled, turned over, and inspected by a retail buyer. There is no concealed face. - **The shape resists rigid holding.** A curved, thin-walled shell has to be gripped firmly enough not to shift during agitation, and firm gripping means larger contact area. - **Hard anodising needs more current.** Type III draws heavily, and a contact that is adequate for a 15 micron decorative coating will heat, arc, or burn at hard anodising current densities. ## Where the mark should land This is a design decision, and the window for making it closes at commissioning. Once the fixtures are fabricated, your options are jig rework or scrap. ### The four viable locations - **Rim underside.** The lip of a kadai or tawa is rolled or curled; the underside of that curl is invisible in normal use and is mechanically strong enough to take a spring contact. - **Handle boss or rivet hole.** If the vessel gets a riveted handle, the rivet covers the mark completely. This is the cleanest solution available and it costs nothing, but it only works if handle position is fixed before jig design. - **Base recess.** Many cookware bases carry an induction plate, a sandwich bottom, or a stamped recess. Anything covered later is fair territory. - **Inside the vessel near the rim.** Least preferred, and only acceptable where a non-stick topcoat will cover it — but be aware the coating over a bare contact point is the weakest adhesion site on the whole piece. ### Where it must not land The external sidewall, the centre of the base, and anywhere on a colour-anodised surface where the untreated patch will read as a light spot against dye. On dyed work the mark is more visible than on natural finish, because the bare patch takes no colour at all. ## Contact design that survives production ### Titanium, not aluminium Aluminium jigs anodise along with the part. After a few cycles the jig itself is insulated, contact resistance climbs, current falls, and coating thickness drifts down across the load without any process parameter changing. The operator sees "thin coating" and increases voltage, which makes burning more likely at the contact. Titanium does not build an insulating oxide in the same way and is the correct material for the contact tips. Aluminium is acceptable for the frame, not the contacts. ### Spring pressure, not friction A part held only by friction will shift when agitation starts. A shifted part loses contact, and because the surface it just grew is an insulator, **it cannot re-establish a current path**. That piece comes out partially anodised. Sprung contacts maintain pressure as the part expands slightly with bath temperature. ### Contact area is a compromise, not a target Too small and the contact overheats, arcs, and leaves a burn that is far worse than a witness mark. Too large and you have a visible patch. The practical approach is multiple small contacts sharing the current rather than one large one — three points at 120 degrees on a rim, rather than a single clamp. ## Diagnosing marks you already have ### Clean grey patch, sharp edge Normal contact shadow. Too big, or in the wrong place. This is a jig geometry problem, not a process problem. ### Dark burn, rough texture Contact area too small for the current, or contact pressure lost mid-cycle. Check spring tension and titanium tip condition before touching bath parameters. ### Coating thin across the whole load Usually anodised aluminium jigs, not a rectifier fault. Strip and inspect the jigs before you increase voltage. ### Partial coating on random pieces Parts moving during the cycle. Once contact breaks, the oxide already formed prevents recovery. Tighten the fixture, do not extend the cycle. ## The cost of getting it wrong A reject on a visible-surface product costs twice: the revenue is lost, and the power, chemicals and labour were already spent on the piece that gets scrapped. Our [plant cost and payback calculator](/calculators/anodizing-plant-cost) puts an annual figure on each percentage point of reject rate at your configuration — set the archetype to **Hollowware** to size the line the way a cookware plant is actually built. On most hollowware lines that number is larger than any equipment upgrade being weighed at the same time. And it is set by fixture design, which is decided before a single tank is filled. For the wider picture of what a cookware line demands, see [hard anodising for cookware](/applications/cookware-anodising-plant). For rack design across all part types, see [anodizing rack design](/blog/anodizing-rack-design-india). ## Frequently asked questions ### Can anodised cookware be made without any rack marks? No. Anodising requires physical electrical contact with the part, and wherever the jig touches, no oxide grows. The mark cannot be eliminated, only moved to a location that is hidden by a handle rivet, a base plate or a rolled rim, minimised by using several small sprung contacts instead of one large clamp, or accepted in a position the customer will not inspect. ### Why do my anodised pans come out with thin coating across the whole batch? The most common cause is aluminium jigs. They anodise along with the parts, so after a few cycles the jig itself is insulated, contact resistance rises and current falls across the entire load. Operators often respond by raising voltage, which increases burning at the contacts. Use titanium contact tips and inspect them before adjusting bath parameters. ### Where should the rack contact point be placed on a kadai or tawa? In order of preference: under a handle boss or rivet hole where the handle later covers it, on the underside of the rolled rim, or inside a base recess that an induction plate or sandwich bottom will cover. Avoid the external sidewall and the centre of the base, and be especially careful on dyed work, where the bare contact patch takes no colour and reads as a light spot. ### Why do some pieces come out only partly anodised? The part moved during the cycle and lost electrical contact. Because an anodised surface is an insulator, once contact is broken the oxide already formed prevents the part from re-establishing a current path, so it simply stops anodising. The fix is sprung fixtures that maintain pressure as the part expands with bath temperature, not a longer cycle.