Yes, use the wet sponge on cold tip is generally ineffective, but some people still do it, as a "last try to clean the tip before it cools down completely". And on top of that using rather large forces to scrub it off. Not realizing they are just damaging the things (both the sponge by tearing it apart by the force and hardened solder spikes on the tip, as well as the tip corrosion afterwards).

And for the shocks: It is not immediate destruction, just the surfaces wearing out over time by fatigue cracking within the coatings. 300..350 is still somewhat within the limits, for lead free you sometimes need to go up to 400degC (if you need small tip to melt the solder very quickly) and there the shocks become really way greater. Yes, it is not good practice to use that high temperatures for long time either, but that is another topic, sometimes you just need it.
But it is matter of how long the tip will last, not that much whether it survives short term or not, of course it does.

Here is an example of Chinese cheated with the use of low resolution spectral sensor. Not many users today with discharge sources, and this is not very much noticeable with smooth spectrum LEDs.

I suggest to return this meter while still possible. Or sell it to someone who could use it for its intended purpose, measuring light levels with some added benefits of flicker or *rough* spectral balance.

@Medved Any practical examples where cleaning the tip with wet sponge have done *any* harm due to a thermal shock? Or you are just theorizing?

I am doing it all the time for many years since modern soldering tools has become available, with tip temperatures of 320-350C, also it is a standard practice for the industry, no one uses brass shavings seriously, as it is less convenient. More, most soldering stations come with soldering iron stands having wet sponge plate embedded.

Also, there is no point to use a sponge (or be it brass shavings) on a tip with a temperature below water boiling point as the solder will obviously be solid too, and all sorts of cleaning (short of a file or a sandpaper will be ineffective!
 

@dor123 , have you tried the spectrometer with single wavelength light sources? See if the reading on the spectrometer matches with the actual wavelength. For example, a red laser is ~650nm, a green laser is ~532nm, a violet laser is ~405nm, a neon lamp has a peak at 632.8nm. If the values for these are close (+ or - a few nm) then the spectrometer should be correct.
(Don't point the laser directly on the spectrometer, point the lasers on a white wall and place the spectrometer pointed towards the wall looking at the laser dot.)

There is no calibration instructions in the manual.
"Note: The calibration function is restricted to use by metrology institutes only and is prohibited for use by
non-professionals."

If im not wrong, your spectrometer is model LS335. If its of any help, try downloading the manual for it here.

Ask the seller, they are often helpful

I don't know how to calibrate this spectroscope.
@RRK, @James, can you help me?

For the wet sponge vs brass wool:

The wet sponge is softer, so less abrasion to the tip, but it cools it rapidly, creating heat shocks. So when still generally acceptable for lead soldering (where the temperatures use to be in the 300degC ballpark), the higher temperatures required for lead free means the shock becomes way more significant problem. Plus if the tip is not hot enough to evaporate the water instantly (when someone is wiping the tip when it is already cooling down - never do that), it promotes corrosion of the iron layer.

The brass wire wool is a bit harder, but still should be softer than a good quality tip, but it does not thernmally shock it. For higher temperature lead free soldering (around the 350degC tip) this becomes very important.

Good quality tips use way more than 2 or 3 layers, usually the copper body is coated with Ni (via some intermediate) to get hard, strong surface, mainly at the high temperatures, with iron coating on top of it to form a  layer easilly wettable with molten solder. Nickel alone forms rather hard oxide layer on it (that normally is what protects it against further corrosion), which makes it hard for the solder to adhere to.

So in other words quite complex structure for any DIY.

The "900" style is so common, you can find all kind of tips for it, from really bad garbage till really good quality, obviously more expensive, ones.
Don't forget this format has its origin as a rather good quality and also not that cheap stations, so good quality tips are still made for it.
Only because it became a format chosen for cheepeese clones, the market is also flooded with garbage quality product offerings you have to dig through...

Over the past two years, we have replaced 4 EOL bulbs. All four bulbs are LED bulbs, but there is a significant difference in their lifespan. The bulb with the longest lifespan was installed in early 2017 and worked normally until the beginning of last year. Calculated based on a daily usage of 4 hours, it has used for approximately 12,000 hours before EOL, exceeding the nominal lifespan of 10,000 hours. The bulb with the shortest lifespan is a Philips CRI 90 10W bulb manufactured by Signify. It was installed in March 2025 and was used for five hours every day. It EOLed in October of the same year and only worked for about 1,000 hours, which is the worst bulb I've ever used (Even worse than any of the CFLs and Incandescent lamps used in my home). After that, I replaced both of the mentioned bulbs with the same Philips CRI 90 bulbs. However, after only three months, the color of the light from these two bulbs became visibly different. This is sufficient evidence that the Philips bulbs currently sold in China have very poor quality. I will no longer purchase any Philips LED bulbs for installation in my home in the future. Fortunately, there were no EOL fluorescent lamps in my home in the past two years. Most of them will be replaced with LED modules customized by me this year, and the removed tubes and ballasts will add to my personal collection.