[Milsurplus] Crystal History Book and tips on etching

[Kenneth G. Gordon]

On 1 Aug 2022 at 10:17, Dennis Monticelli wrote:

> 
> There's been some responses to my original posting so to answer a few questions and provide 
> more detail: 
> 
> The blanks do not have cracks (or other flaws such as crystal twinning) when they are built and 
> should they develop cracks due to excessive drive later the crystal is ruined.  The etching process 
> does not leave behind the weakly attached debris of mechanical polishing.  It will quickly remove 
> the debris of mechanical polishing
> 
> Yes, I am using ammonium bifluoride crystals  A friend gave me so I don't know where to buy 
> them.  In solid form the material is easy to store and relatively safe to handle while preparing the 
> solution.  The crystals are dissolved in water as needed to produce whatever concentration one 
> wants.
> 
> I used Whink back in the 60's when I was a novice.  It works.  It contains stuff other than HF so 
> make sure you clean the blank well.  Actually, that applies to any method of crystal reduction.
> 
> I make up a solution in a plastic pill bottle and place a support structure for the blank inside.  I use 
> a cutoff piece of an old all-plastic hair brush placed bristle side up in the bottle.  That way the 
> blank can rest on the bristles and the solution can access both sides evenly.  I usually swirl the 
> bottle every few minutes to assist that process.  Using plastic tongs and gloves I remove the 
> blank, swish it through tap water bath #1 (change this bath frequently), then tap water bath #2, 
> and finally distilled water bath #3.  Then blot the excess water and place in the holder for testing.  
> When the final frequency is achieved I use a final final wipe down of the blank with a Q tip soaked 
> in isopropyl alcohol.  I dispose of the small amount of depleted solution by first diluting it with 
> water in a 5 gal plastic bucket.
> 
> Note that whether grinding or etching the material removal technique only applies to crystals that 
> resonate in the thickness-shear mode,

...and this fact explains why some broken crystals can still work...

> which includes FT-243, CR-1/A and most of the 1930's 
> types. The former are AT cut and the latter are typically Y cut.  I try to limit my frequency moves to 
> about 25Khz or less (relative to 7MHz).  Moving 100KHz in my humble experience often results in 
> a loss of activity.  
> 
> Dennis AE6C

Thank you for all of the above, Dennis. My results pretty much match yours. 

I HAVE found that when activity of an etched crystal drops, that activity can be restored about 
50% of the time by grinding all 4 edges, then recleaning.

Although I don't know for certain, I suspect that etching "rounds off" the edges thereby 
causing some sort of strange interference which prevents the crystal from oscillating.

Ken W7EKB