How to choose a dye penetrant system
By Grant, Inspection Tool Specialists. Reviewed November 2026.
Three things decide which dye penetrant system you need: the surface and material you test, the smallest crack you must find, and the temperature and place of the test. Answer those first, because a penetrant chosen for the wrong surface or temperature will miss defects.
Dye penetrant testing finds cracks and other defects open to the surface on non-porous materials, including most metals, plastics and ceramics. It does not find defects below the surface.
How the process works
The surface is cleaned and dried. Penetrant is applied and left to dwell, during which it enters any open crack by capillary action. The excess is removed, the developer is applied, and the developer draws penetrant out of the cracks so they show as indications. Each step has a time or temperature limit that your procedure sets, and you must follow it.
Water-washable, solvent-removable or high-temperature?
| Type | How the excess is removed | Suits | Typical in our range |
|---|---|---|---|
| Water-washable | Rinsed off with water | Quick, simple checks, including on site | MR311-R; MR68NF |
| Solvent-removable | Wiped off with a cleaner | Rough or large surfaces where a water rinse is hard to control | MR62 with MR79 cleaner |
| High-temperature | Remover suited to hot surfaces | Hot parts and components where standard penetrants are unsuitable | MR68H with MR70H developer and MR91H remover |
| Fluorescent | Depends on the penetrant type, read under UV-A light | Higher sensitivity, for finer cracks | MR672F (level 2); MR653F (level 3); MR67 red and fluorescent |
Sensitivity: how fine a crack must you find?
Penetrants are graded by sensitivity. A higher level finds finer cracks but costs more and needs a darker inspection area for fluorescent indications. Choose the level from the smallest defect your procedure or specification requires, not the one that sounds best.
Developers must match the system
The developer should come from the same system as the penetrant. White developer shows red penetrant on a white background; a dry fluorescent developer powder is used with fluorescent penetrants. Mixing systems from different suppliers can change the sensitivity of the result, so buy the penetrant, cleaner and developer as one set.
Verify the process
Check the process on a known flawed specimen before you rely on it for production parts. Our NDT standard flawed specimens kit covers dye penetrant among other methods, and it is a useful reference for training and for proving a process.
Which system should I buy?
| Application | Suggested starting point |
|---|---|
| Quick water-washable checks | MR311-R water-washable penetrant (confirm the matching developer for your procedure) |
| Solvent-removable on rough or large surfaces | MR62 solvent-removable penetrant, MR79 cleaner and MR70I developer |
| Finer cracks, fluorescent | MR672F level 2 or MR653F level 3, with the MR81T-R dry developer |
| Hot surfaces | MR68H high-temperature penetrant, MR70H developer and MR91H remover |
As a guide to our current range, including VAT: penetrants from about R1,850 to R6,820; developers from about R900 to R7,340; high-temperature systems from about R7,340; the standard flawed specimens kit is about R28,600. Prices change, so check the product pages and confirm each system is complete for your procedure.
Questions we will ask you
Tell us the material and surface finish, the smallest crack you must find, the temperature of the part, whether you test on site or in a workshop, whether you need fluorescent or visible indications, the procedure or standard you work to, and the records you must keep. With that we can recommend a system and provide pricing.