What color does the oxygen indicator change to, and can it change back? Tianhua receives both questions from customers. Some want an irreversible response because they are concerned about what happens after a pack leaves the factory.
The answer depends on the model. Liquid Type B changes from green to yellow and is irreversible; Tablet Type P is reversible. Even pink has different meanings: it signals low oxygen on the standard visual indicator, but higher oxygen on Type P.
Start with the model and its color guide, then decide when and where you will inspect it. The six checks below help prepare a sample inquiry. They are not a validated test protocol.
1. Say whether you need an indicator, an absorber or both
For the sample request, the distinction is straightforward: the indicator gives a visible oxygen signal, while the absorber removes oxygen. Ordering one does not specify the other.
If an absorber is already part of your pack, include its details with the indicator inquiry. The trial then has a record of both components rather than a vague description such as “oxygen-control sample.”
Decide what the inspection must establish. A visual check needs the correct color guide. A decision based on a numerical oxygen concentration needs a suitable quantitative measurement method too; the color is not an exact gas reading.
2. Use the color guide supplied for that model
The Tianhua oxygen indicator catalog lists these descriptions:
| Option | Published color description | Response description |
|---|---|---|
| Standard visual indicator | Pink at low oxygen; blue at higher oxygen | Reversibility is not stated in the supplied material |
| Liquid Type B | Green to yellow | Irreversible |
| Tablet Type P | Purple at low oxygen; pink at higher oxygen | Reversible |
Pink therefore cannot be a stand-alone acceptance rule across these options. A record needs the model and instruction revision beside the observed color. Otherwise the next reviewer has to guess which guide the inspection used.
For the standard option, the supplied material does not say whether the response is reversible. Leave that as a question for the supplier rather than borrowing Type P’s description. Likewise, a catalog description is not a result from your packaging trial.
Request the current reading conditions for the actual sample model. The table separates the published options; it does not replace their instructions.
3. Define when the sealed pack will be inspected
Choose the inspection point before requesting samples: at dispatch, after transport or during storage. Put it in the brief alongside whether the response needs to be reversible. The supplier then knows what you want to observe and when you need to observe it.
Type P can change back, so a later observation is not a permanent record of earlier exposure. Type B changes irreversibly, but a changed color does not date the event. For either model, retain the sealing time, observation time and pack identifier with the photograph.
There is no fixed reading time for all these options in the catalog. Plan the observation interval using the selected model’s instructions and your agreed trial conditions.
4. Check the view through the filled pack
Where will the inspector look? Mark the proposed indicator position on a pack drawing or photograph. Then check it through a representative sealed pack, with the contents in place. Printed film or the contents may obscure a spot that looked suitable on an empty bag.
Package dimensions alone will not show that obstruction. If a trial changes the position, note it with the result rather than attributing every difference to the indicator model.
Tell the supplier whether the packing process uses vacuum, gas flushing or an oxygen absorber. Include packing, storage and transport conditions. These are inputs for a review of the model’s handling and operating limits, not evidence that the model will suit the application. A shared catalog value should not replace its own instructions.
5. Identify the application and supporting file
For Tianhua oxygen indicators, the food line is Oxyfree and the pharmaceutical line is MedShield. Tianhua Tech manufactures both. “504” identifies a product series; the sample still needs its specific model name.
For a food pack, the document request should describe the intended position, any planned contact with the contents, and the destination market. A company certificate by itself does not establish suitability for that component and use.
Pharmaceutical component review belongs with the responsible quality team. The indicator supplies a visual oxygen signal, not proof of medicine stability or sterility. The same distinction applies to food safety: a color does not establish it.
6. Send a brief that can stay with the samples
Include these details in the inquiry:
- Product and food or pharmaceutical application.
- Package material structure and dimensions, with the proposed indicator position.
- Packing process and any vacuum, gas flushing or absorber use.
- Inspection point, storage conditions and transport conditions.
- Requested model, or the options you need help comparing.
- Supporting documents required by the packaging or quality team.
Ask for the exact model, lot details, current color guide, response conditions and handling instructions with the samples. For each trial pack, a pack identifier connects those documents to the observation time, conditions, photograph and interpretation. Add quantitative measurements where the trial plan requires them.
The packaging or quality team must define the trial method and acceptance criteria before testing. An unclear reading can stay unresolved while it is reviewed; there is no need to label it a pass or fail without that review.
Send the sample brief to Tianhua. A drawing or photograph is useful where words cannot show the intended placement. Keep the supplied model’s instructions with the trial record, so the next inspection uses the right color rule.