The prices of infrared temperature sensing devices have plunged in recent years. They provide temperature readings by reading infrared radiation from objects. For quantum mechanics reasons, metal surfaces have low emissivity, making this a poor system for metal objects.

Brass espresso machine parts typically are coated with a polymer to prevent surface oxidation. This polymer surface emits infrared quite well, so one can measure the surface temperature of the parts of coated surfaces.

One can place pieces of tape over chromed or other metallic surface and read the temperature of the tape. Most infrared radiation thermometers have a laser to locate the area where the sensor reads. Mine is points to the TOP, not centre of the area read. The sensor seems to read a circle with a diameter of about five or six degrees. (But with it close the diameter seems to be greater than about 2 cm.) The device reads the entire circle, so it must be pointed carefully.

My real copper and brass 1999 La Pavoni Europiccola is coated, except the boiler came bare metal, and I stripped the coating from the portafilter because its polymer coating was peeling badly. My 2012 "brass" Microcasa a Leva is polymer coated everywhere.

My 1964 La Pavoni is bare chrome. To measure temperatures on it requires sticking pieces of tape on the location to be measured, being sure that the tape is large enough to take in the measured area. Other chrome surfaces will, of course, have the same problem.

It is highly instructive to take a coated brass machine and explore its surface with one of these devices. This can be done with a chrome plated machine, but ones needs to stick tape over all the surfaces to be measured!

The surface temperature is going to be lower than inside because the surface is losing energy by both conduction to near by air and radiation. Heated air is less dense, so it rises and sets up convection currents near the surface with enhance the conduction loss.

I hate wires running all over the place, and this, it seems to me, is a far better way to measure temperatures at least on polymer coated brass or copper surfaces. It also allows scanning entire coated brass machines like some MCALs.

I had my finger on the trigger to buy an IR thermometer but did not pull it because of this...
Still am wondering if the looking glass of the faemina would be a good spot to take the measurments, also could use it for my pizza oven experiments (check the modding of my ferrari g3)
Sticking huge dots of imo ugly tape on my faemina is not what I want, as I'm sure it is pure chrome and not coated (1954), do you happen to know if IR works reliable on glass ?

The IR thermometer measures incident IR energy or radiant heat in the common parlance. There are books that list the emissivity at given temperatures. Thermal imaging is a big part of non intrusive predictive maintenance in electrical generating plants and has been for better than 20 years. Relative temperature differences are easy to detect but absolute values are not. A high carbon pigment percentage flat black paint will get you the closest to the actual temperature of whatever it is applied to.

Glass has a high emissivity, over 0.9. The very nature of metals makes their emissivity very low. Most other materials have quite high infrared emissivity. Polymers have high emissivity too. That is why the coating applied to brass can be used. Thus one could read temperature from a glass surface. (But one cannot measure through a glass because IR of most wavelenghts is strongly absorbed by glass. Infrared spectrometers have to use salts for optical parts!)

Thick oxide coatings on metals can result in high emissivity. Anodised aluminium has moderately high emissivity. It is the SURFACE that is involved.

Reading temperatures this way has really two sources of error: (1) emissivity variation--if too low the indicated temperature will be too low, and (2) you are measuring the surface from which energy is being lost by radiation and, unless under a vacuum, convection. (Convection is really conduction to a moving fluid.) Hence surfaces are cooler than the inside of an object.

(The latter error is also present and at least as severe with temperature sensors attached externally to objects. That is why scientific instruments have "thermometer wells".)

A chrome plated espresso machine with pieces of tape stuck all over it all the time would be a bit ugly. (Maybe more than a bit!) But one could put it on for measurement and take it off again.

I found that the temperature read from the outside of a metal boiler and the inside surprisingly close and therefor not that highly influenced by typical changes in home ambient conditions. Perhaps someone has some data points from accurate devices.

As long as the readings are the same every time , its not such a big deal if the true value is of

if the shoot tastes good at 89 , better at 90, and best at 92 READINGS , then one just go for that value

as long as the reading are constant

one can ad a a small, stick to the meter , then imply , touch the what ever to test , you would have the same distance every time , and that is what really can get the reading of (different distances )

But a dark spot really helps , i did once try to get a reading on bare chrome , it was low , then i did hold my hand next to the machine , and pointed the meter at the mirror image of my hand showing in the chrome ,,well i got a reading of the temp of my hand ;o)

I have both ranges of Omega temperature strips stuck to my Gaggia Factory as well as a digital thermometer with the thermocouple junction tucked under a group head gasket against the back of the group.

However, for my Faemina I'm in the same boat as Marcelnl, I have not added any thermometry at all, preferring the classic look of this espresso machine. I've found that with the pressure release valve set to 0.3 bars, the Faemina is pretty stable and I don't feel the need or urge to add anything to it.

I have an IR thermometer in my backpack that I use for work (to make sure that the environmental temps at communications sites are within a normal range) but so far have not been too tempted to try to use it on my Faemina.

I use the IR thermometers for measuring temps that are not super accurate but just for general reference. On the espresso machines I measure the temps of the tubing coming right out of the boiler, the boiler itself, and the backside of the group (shiny stuff does not read well). You can also measure the water being flushed from the group to get a rough idea of what happening and compare that to the boiler readings.

You can measure wire temps too and that was why I own the device.