A thermal printer must know where one label ends and the next label begins. It normally identifies this position using a gap, black mark, notch, hole or another supported media-registration method.
If the physical label construction does not match the printer's sensing capability and settings, the printer may skip labels, feed continuously, stop in the wrong position or print across two labels.
Before purchasing label media, confirm the exact printer model, supported sensor type, label dimensions, registration method and feed direction.
How does a thermal printer know where each label starts?
Thermal printers use a media sensor to identify a repeatable change in the label web.
Depending on the printer and label construction, the sensor may detect:
- The exposed liner between die-cut labels
- A black registration mark
- A notch or hole
- A continuous web without individual boundaries
The selected media mode must describe the labels actually loaded in the printer. A printer set for gap media may not correctly detect black-mark labels, and a printer set for continuous media will not necessarily stop at every die-cut label.
What are gap thermal labels?
Gap labels, also called web labels, are die-cut labels separated by a small area of exposed liner.
The gap creates a measurable change between:
- The area containing both the label and liner
- The area containing only the liner
Many thermal printers use a transmissive sensor for this media. A light source and detector are positioned on opposite sides of the media path. The printer measures the change in light passing through the label web as each gap moves across the sensor.
Gap labels are commonly used for standard shipping, warehouse, inventory and barcode applications.
Successful detection still depends on:
- Printer support for gap or web sensing
- Gap dimensions
- Liner opacity
- Label shape
- Sensor location
- Media alignment
- Correct calibration
There is no universal gap dimension that works with every printer. Compare the complete label specification with the exact printer manual.
What are black-mark thermal labels?
Black-mark labels use a dark registration mark printed at a repeatable position, commonly on the underside of the liner or media.
A reflective sensor emits light toward the media and measures the reflected signal. The black mark produces a different response from the surrounding area, allowing the printer to identify a registration point.
Black-mark media may be used when:
- The printer and application are designed for reflective sensing
- The material is difficult to detect with a transmissive gap sensor
- The media is opaque
- The label shape or construction requires a defined registration mark
- A continuous-looking face stock needs repeatable print positioning
- The equipment specification requires a black mark
The black mark must match the printer's requirements for location, width, length, contrast and repeat distance. The sensor must also be physically aligned with the mark as the media feeds.
Gap vs black mark: what is the difference?
The main difference is the physical feature the printer detects.
- Gap media: The printer detects the change between the label area and exposed liner.
- Black-mark media: The printer detects the contrast between a printed mark and the surrounding media.
Neither method is automatically better. The correct choice is the method supported by the printer and appropriate for the label construction.
What are notch and hole labels?
Some media uses a notch or hole as the registration feature.
The cutout must pass through the usable sensor path. Depending on the printer, notch or hole media may require a specific sensor type, setting and physical alignment.
Before ordering, confirm:
- Notch or hole position
- Dimensions
- Distance from the media edge
- Repeat length
- Sensor adjustment range
- Feed direction
- Printer media setting
A notch near one edge of the liner is not useful if the printer's sensor cannot move into that position.
What are continuous thermal labels?
Continuous media does not contain a gap, black mark, notch or hole defining each individual label.
The print job and printer setting control the printed length. Depending on the equipment, the media may be torn manually or cut after printing.
Continuous media can be useful when variable lengths are required, but the printer must explicitly support the format and intended cutting or tear-off method.
Do not select continuous mode for ordinary die-cut labels unless the printer documentation or workflow specifically requires it.
How do transmissive and reflective media sensors work?
Gap and black-mark media normally use different sensing principles.
Transmissive sensing
A transmissive system has a light source on one side of the media and a detector on the other side.
The printer measures how much light passes through the loaded material. The response changes when exposed liner instead of label-plus-liner passes through the sensor path.
Possible detection problems include:
- Opaque or unusually dense liner
- Pre-print interfering with the sensor path
- Very small or inconsistent gaps
- Sensor positioned away from the gap
- Media drifting sideways
- Dust or label residue near the sensor
Reflective sensing
A reflective system emits light toward the media and measures the reflected signal from the same side.
The black mark creates a strong contrast with the surrounding area. The mark must pass directly through the reflective sensor path.
Possible detection problems include:
- Mark positioned outside the sensor range
- Mark dimensions outside the printer specification
- Insufficient contrast
- Incorrect winding or feed direction
- Printer configured for gap instead of mark media
- Other printing on the liner creating false readings
Sensor designs vary. Use the exact printer manual rather than assuming every model places its sensors in the same location.
Which format is used for standard 4×6 shipping labels?
Many standard die-cut 4×6 shipping labels use gaps between labels, but this is not universal.
Before purchasing, check:
- Gap, mark, notch or continuous sensing
- Minimum and maximum label width
- Label length
- Gap or mark dimensions
- Media sensor position
- Roll or fanfold support
- Core size and maximum roll diameter
Do not order only by the description “4×6 thermal labels.” Two products can have the same printable area but different liners, gaps, black marks, winding directions or roll configurations.
Are gap and black-mark labels available in roll and fanfold formats?
The supply format and sensing method are separate specifications.
- Roll or fanfold describes how the labels are supplied and fed into the printer.
- Gap, black mark or notch describes how the printer identifies each label position.
A roll and a fanfold stack can both contain die-cut labels separated by gaps. A special roll or fanfold construction may also use black marks when the printer and application require them.
Confirm both specifications before ordering.
Does direct thermal vs thermal transfer affect gap sensing?
Direct thermal and thermal transfer describe the printing technology.
Gap, black-mark, notch and continuous describe media registration.
A complete label specification should confirm:
- Printing technology
- Label material
- Adhesive
- Label dimensions
- Roll or fanfold format
- Core and roll dimensions
- Media-registration method
- Winding and feed direction
A direct thermal printer can still require gap, black-mark or another supported sensing method.
Why is my thermal printer skipping labels?
Skipping labels does not automatically mean the label stock is defective. Begin by confirming that the media and printer settings match.
1. Identify the loaded media
Inspect both sides of the media and record:
- Label width and length
- Gap size
- Black-mark location and dimensions
- Notch or hole position
- Label pitch or repeat length
- Feed direction
- Roll winding direction
2. Confirm printer support
Check the exact printer model—not only the brand.
Confirm whether it supports:
- Transmissive gap sensing
- Reflective black-mark sensing
- Notch or hole media
- Continuous media
- A fixed or movable sensor
- The required label width and repeat length
Two printers from the same brand may support different sensor locations or media specifications.
3. Select the correct media mode
Set the printer to the method used by the labels:
- Gap or web
- Mark
- Notch or hole
- Continuous
Check the printer panel, driver and label software. In some workflows, the driver or print job can override a setting stored in the printer.
4. Align the sensor and media guides
If the printer has a movable sensor, align it with the physical registration feature.
Also check that:
- Media guides prevent excessive side-to-side movement
- The label roll or fanfold stack feeds straight
- The black mark or notch remains in the sensor path
- The sensor area is free of dust, liner pieces and adhesive residue
Follow the printer manufacturer's instructions before cleaning sensor components.
5. Calibrate the printer
Calibration allows the printer to measure the loaded media and learn the label repeat.
Use the calibration procedure for the exact model. Button sequences and manual-calibration steps vary between printers.
The printer may feed several labels during calibration. Confirm the expected behavior in the model manual.
6. Verify the size settings
Make sure the print file, driver and printer use compatible values for:
- Label width
- Label length
- Gap or mark offset
- Orientation
- Print origin
- Tear-off, peel or cut position
If label length is confused with label pitch, the print position may gradually drift.
7. Print a controlled test batch
Print several labels and check:
- One-label feed behavior
- Starting position
- Vertical alignment
- Whether blank labels are skipped
- Whether the image drifts during the batch
- Whether the printer reports a media-out error
Change only one variable at a time and record the result.
What is label pitch?
Label pitch is the repeat distance from a point on one label to the same point on the next label in the feed direction.
For ordinary rectangular gap labels, pitch generally includes:
- Label length in the feed direction
- Plus the gap between labels
The printer may use this repeat measurement during calibration and positioning. Do not confuse label length, gap size and total pitch when specifying custom media.
How should black marks be specified?
A black-mark specification should include more than the words “black mark.”
Record:
- Mark width
- Mark length in the feed direction
- Distance from the media edge
- Distance from the label edge
- Repeat distance
- Side of the liner or media carrying the mark
- Required contrast or density when specified
- Feed and winding direction
Use the printer manufacturer's stated limits. A mark that works in one printer may be outside the usable sensor range of another model.
Can pre-printed graphics interfere with the media sensor?
Yes. Printing on the front of the label or back of the liner can enter the sensor path and create a false reading on some systems.
If pre-print is required:
- Identify the sensor path before artwork approval
- Keep critical sensing areas clear
- Confirm the printer's recommendations
- Test the final printed construction
Do not approve custom pre-print based only on an unprinted sample.
What should I send Volokitx before ordering?
Send:
- Printer brand and exact model
- Printing technology
- Required label width and length
- Roll or fanfold preference
- Gap, black-mark, notch or continuous requirement
- Gap dimensions or black-mark specification
- Core size and maximum roll diameter
- Winding and feed direction
- Labels per roll or stack
- Application
- Estimated monthly usage
- Delivery ZIP code
If possible, include photographs of both sides of the current media and a clear picture of the printer model label.
Should I test a sample before a bulk order?
Yes. A sample should be tested using the actual printer, driver, software and operating settings.
Verify:
- Loading and feeding
- Sensor detection
- Calibration
- Print position
- Batch consistency
- Barcode readability
- Adhesive performance
Approve the complete media specification before ordering larger carton or pallet quantities.
Frequently Asked Questions
Can one printer use both gap and black-mark labels?
Some printers support both transmissive gap sensing and reflective black-mark sensing. Support and sensor position vary by model, and the correct mode must be selected.
Are black-mark labels better than gap labels?
No format is better for every application. Gap labels are common for standard die-cut media. Black marks can provide a defined registration point for compatible printers and specialized constructions.
Why does my printer feed one blank label before printing?
Possible causes include media synchronization, calibration, sensor mode, label size settings or a print job that starts after the printer locates the next registration point.
Why does the print position drift down each label?
Drift may occur when the printer is not consistently detecting the gap or mark, when label pitch is set incorrectly or when calibration and driver settings do not match the media.
Can I add black marks to ordinary labels myself?
Manually adding marks is not a reliable production specification. Mark placement, dimensions, contrast and repeat must remain consistent and match the printer.
Do fanfold labels use a gap sensor?
Many fanfold labels are die-cut with gaps and can use gap sensing, but fanfold describes the supply format rather than the sensing method.
Does the perforation tell the printer where to stop?
Not necessarily. A perforation is primarily a tear line. The printer may use a separate gap, mark, notch or other registration feature.
