Ano
Article · Color
Why Does Black Anodizing Look Different Between Batches?
Because dye takes according to how the base coating came out. Coating thickness, dye time, bath chemistry and seal condition all drift, and every one of them moves the shade. Holding color is recipe discipline rather than better dye.
Why the Shade Moves
Color in an anodized part does not sit on the surface. Dye is drawn into the pores of the oxide coating and then sealed in, so the amount of dye a part accepts depends on how the coating itself came out.
Change the coating thickness and the depth of color changes. Change the dye time or the dye bath concentration and it changes again. Change the seal and the finished appearance shifts once more. None of these has to move very far to produce a visible difference between two batches placed side by side.
The Part That Is Not the Shop's Fault
Alloy and heat lot. The coating is transparent and takes on the character of the metal underneath, so parts cut from a different alloy, or from a different heat of the same alloy, can finish visibly differently even when the process was identical.
High-copper alloys such as 2024 finish darker and less uniformly, and high-silicon casting alloys finish gray and mottled. Those are permanent material properties. The alloys guide covers what to expect from each.
What a Shop Should Be Doing About It
Recording the recipe and running to it. Coating thickness, dye time, dye concentration and seal conditions from your first order should be written down and referenced when the reorder arrives, so batch fifty matches batch one instead of nearly matching it.
The batch should also dye together and seal together so parts match each other within an order. And where a customer has parts that must match across a set, the shop needs to know that before the job runs, so they can be run together.
What to Do if You Already Have Mismatched Parts
First establish whether the difference follows the parts or the position. If the mismatched parts came from a different material lot or a different alloy, the cause is metallurgical and re-running them will not reliably fix it. If they were the same material, it is process drift and a re-run stands a good chance.
Second, be realistic about stripping. Removing an anodic coating takes base metal with it, so dimension-critical parts may not survive a strip and re-run. On non-critical parts it is usually straightforward.
Third, if the parts are for an assembly where only relative match matters, running the whole set together is far more reliable than trying to hit an absolute target twice. That is the single most useful thing a customer can tell a finisher: not what shade, but which parts have to match each other.
Common Questions
Can Black Anodizing Be Matched Exactly Across Reorders?
Within the limits of the process and the material, yes, and it comes down to keeping the recipe from the first run and referencing it. We do that as a matter of course, which is why reorders here match instead of nearly matching.
Why Is My Black More of a Dark Gray?
Usually a thinner coating, which gives the dye less depth to sit in, or a Hard Coat where the dense coating is naturally dark rather than deeply dyed. Alloy plays a part too, particularly on high-copper material.
Will Black Anodizing Fade in Sunlight?
Sealed black is stable in normal service. Long-term direct sun can soften some organic dyes over years, so tell us if the part lives outdoors and dye selection accounts for it.
Can You Match a Shade Another Shop Produced?
Sometimes, and it is easier if you send a physical sample rather than describing it. What we will not do is promise a match we cannot confirm on your alloy, so we check before quoting instead of after running.
Do Type II Black and Type III Black Look the Same?
Not quite. Type II black is a smooth satin black. Type III black is harder and slightly more matte, because the dense Hard Coat is naturally dark before dye is considered. If parts of one assembly use both, expect a visible difference.
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