Two quantities, two starting conditions
A Sketch marker that still contains ink and a new empty Sketch marker are not the same vessel to fill. Copic lists around 1.8 ml as its Sketch refill guidance. On the same product site, the instructions for preparing an empty Sketch marker with custom ink give about 3 ml. Taking the larger number from the empty-marker instructions and applying it to a partly used pen misses that distinction.
The Copic Ink page makes the reason explicit: recommended refill amounts are lower than the ink content of new markers to avoid overfilling. It also says to check fullness each time ink is added. Treat the number as guidance for its stated job, not an instruction to add the same dose whatever remains inside.
Use the documented opening
For an ordinary refill, Copic’s sequence is to uncap both ends, use the tweezer tool to pull the broad nib from its base, place the long ink nozzle into the marker’s core and squeeze gently. The nib goes back after refilling. This is a brief description of the maker’s method; keep its illustrated instructions at hand when doing it.
The ink is alcohol-based and flammable. The manufacturer calls for ventilation, keeping it away from direct sunlight and excessive heat, and keeping it out of children’s reach. A tidy place for refilling therefore needs more thought than whether the bottle will fit into the pen case.
Ink and a replacement nib solve different purchases
Sketch comes with Super Brush and Medium Broad nibs. Copic distinguishes the Sketch/Ciao replacement family from Classic, so a packet bearing the same brand name is not enough to establish fit. Before ordering, identify whether you actually need matching refill ink or the correct replacement nib for a worn or damaged tip. A pale stroke alone is not a reason to buy every maintenance item at once.
Sources & further reading
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