How do I cross search multiple keyword items?

My client has about 100 chemical publications put into our Joomla install. They've asked me to build a search that has 3 text area search fields: Year, Chemical, and Author. They want the web visitor to be able to run a search against the Publications by putting keywords into the fields.

So they might search for: 1992, benzene, Smith. So all three fields need to filter the search results by year, chemical name and/or author's name. How do I make the search do this?

You need 3 Cp fields: [Year], [Chemical], [Author]

1) Enter all possible years as values for the [Year] field. This is a good candidate for a 'text' field type.
2) Enter all chemicals names as values for the [Chemical] field. This would likely be an autocomplete or a multiselect with picker interface field type.
3) Enter all authors names as values for the [Author] field. As above.
4) Assign tags to publication articles (it works also with K2 items).
5) Publish the cpsearch module.
6) Enjoy

So if I'm understanding you correctly, I have to go into each of the 150 articles and add tags for cross-filtering to work? If the words are already in the article, won't that work as a tag?

Adding tags to 150 articles is going to be an insane amount of work. Is there any other way? Like would 3 free text fields work in cross-filtering?

So if I'm understanding you correctly, I have to go into each of the 150 articles and add tags for cross-filtering to work?

Yes, you have to.

If the words are already in the article, won't that work as a tag?

No they won't. Tags are more accurate.
Custom Properties lets you perform a keyword search on title, introtext and fulltext fields. The query mode is selectable (all words, any words, exact phrase). However, searching by tags is MUCH more accurate. E.g. the text of the article might contain a series of digits that can be interpreted as year of publication while insetat it's part of some formulas. The text could also contain references to chemicals unrelated to book itself (i.e. chemical product ALPHA (unlike chem product BETA) has properties such and such.)

Adding tags to 150 articles is going to be an insane amount of work. Is there any other way?

We do not have first hand experience in this field, but we've witnessed *thousands* of articles tagged in a short period of time. The job can be done in one day, tagging 20 articles in one hour.

Is there any other way? Like would 3 free text fields work in cross-filtering?

As I wrote above a text search will work, but the quality (relevance) of the results will be totally underwhelming. (BTW, you could be using the standard Joomla search and avoid CP altogether).

Just to jump in here and say I found the tagging of masses of articles pretty easy using the 'Assign Custom properties' tab.

I then using the section and category filters to help group the articles I needed tagged.

Using the tick boxes to select all the items and tagging all of them at once from there.