Are there any materials, such as a type of tempered glass, that can not be drilled or penetrated by any means (steel drills, diamond drills, saws, lasers, ablation with focused ion beam machines, etc) without some sort of dramatic evidence of such drilling (cracks throughout the entire piece, or a dramatic change of color of an area covering several square centimeters, etc)?

If not, are there materials that can not accept holes over a certain size, but that will accept smaller holes? For instance, maybe there is a material that can accept 50 micron holes but not 1mm holes.

The machinist may or may not have access to a full-fledged laboratory with million-dollar equipment, including things like focused-ion beam machines. If there is a material that resists attacks using inexpensive machines (under $100,000) but not things like focused ion beam machines, that would still be interesting to me.

Additional info:

My goal is to build a tamper-evident container about the size of a brick, perhaps 120mm x 120mm x 180mm. That rules out some materials, such as nitrogen triiodide, which can not be used to make containers.

I'm aware that there are existing ways of building these containers using electronic sensors connected to something, such as a random arrangement of printed wires encased in epoxy, or some sort of mechanical trigger. I seek to develop a more sensitive scheme that is harder to bypass by having the container itself be made out of a material that amplifies the effect of an intrusion attempt.

I'm pretty familiar with tamper-evident seals, and find they all are either pretty easily defeatable (i.e. in a lab setting; perhaps they are good enough for particular field applications), or require detailed non-automated inspection to determine tampering (such as requiring the detailed comparison of before & after photos, as I hear is done using random solder and wire-brush marks on some nuclear program auditing seals). I am also familiar with some micro-level tamper-evident schemes, such as putting an additional patterned metal layer on a chip, with capacitive sensors on the layer below to sense tampering.

I realize these sorts of clever electronic or mechanical schemes can provide some degree of tamper evidence. Lately I've become curious if these traditional approaches can be improved upon by deploying a special material that is inherently tamper evident.

  • 3
    $\begingroup$ Have you done any research on the topic? Right now, this is more of a "find me references question," which isn't on-topic for this site. Also, if we knew what exactly you were trying to achieve with this material, it might be helpful in pointing out something that will work. $\endgroup$
    – grfrazee
    Commented Dec 10, 2015 at 20:12
  • $\begingroup$ There is no material whose shape resists changing for all machining processes, though there are orders of magnitude difference in time taken. Diamonds can be fractured by impact, and even glass will wear away - that's where sand comes from. There are also two questions here: (1) what are machining-resistant materials? (2) where can I learn more about machining-resistant materials? Since we don't answer questions of the latter type, you might edit your question to only ask the former. $\endgroup$ Commented Dec 10, 2015 at 21:02
  • $\begingroup$ I'd also like to add that, generally, material properties are by definition geometry independent. Put another way, material properties should be properties of only the material, not of the material and how it is shaped, used, test, etc. There are several organizations and thousands of detailed documents whose purpose is to standardize the testing of materials, so that "all-else-equal" comparisons may be made between different materials: i.e. isolating the material properties, instead of test setup artifacts. See ASTM and NIST. $\endgroup$ Commented Dec 10, 2015 at 21:06
  • 3
    $\begingroup$ Fluids can't be sawed or drilled $\endgroup$
    – DLS3141
    Commented Dec 11, 2015 at 15:56
  • 2
    $\begingroup$ You could create a thin plastic layer filled with hydrofluoric acid, such that any significant impact breaks the plastic, allowing contact of the acid with the metal case. HF won't dissolve the steel, but it will damage it, leaving visible marks. Also, HF is crazy poisonous, so it comes with the added advantage of probably killing whoever damaged the case. A dead body next to your case is usually a good way to make tampering quite evident! $\endgroup$
    – Wasabi
    Commented Dec 12, 2015 at 23:02

2 Answers 2


You may want to reword your question. What you are looking for is tamper evident materials or tamper evident technology. Searching for those may give you some better results.

Be aware that anyone with enough time and money can defeat tamper evident materials/designs. I am not sure what you are building, but you may want to consider a non-passive system such as a computer based machine lockout or internet based web reporting of the violation.

Tempered glass is a good one. It is manufactured with built in stresses. If you attempt to drill or cut it, the whole sheet will explode into small peices. There may be an exotic way to cut it, but like you mentioned it would not be cost effective.

Another example would be tempering metal or quenching it. A material that was easily machined before can be made very hard and difficult to machine.

There are other non-reversible processes that may be of interest too.

Shrink fit assembly involves heating the large part or cooling the small part and easily fitting them together. Once they are the same temperature it is almost impossible to cleanly remove.

Epoxy potted circuit boards are difficult to tamper with.

Fiber filled composites and gummy metals paired with very hard metals or ceramics are very hard to saw because the saw tends to bite in and break teeth quickly. Slow working abrasives are usually used for those purposes.


Try an extremely tough material on the outside, and an very fragile material on the inside which contains microprint, or some other information not easily replicated.

No material is impenetrable, so the idea would be to make it very difficult to break the outside while being sufficiently gentle with the inside.

Assuming you succeed in that, you will then have to make sure the fragile indicating liner cannot be simply replicated and replaced. For that you will need it to contain some time of information throughout that is destroyed if the liner is destroyed.

Really, storage of unknown information within the container itself is the critical part here, because if we look at this as a thought experiment, it will generally be possible to replicate the container entirely, thus eliminating any evidence that it was opened.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.