Understanding Color change Intensity

[Bonsai]

What determines if a color change is moderate, intense etc? I am assuming the gems complete change to the color but how does the lighting matter .

EX:
I have an alexandrite necklace and ring.
Both have GIA reports.
Necklace is an oval changing from yellow green to purple (gia report)
Ring is a round changing from blue green to purple (GIA report)

I notice however in the lighting there is a big difference between how quickly they change

the necklace will change colors when an incandescent light is held over it from a distance. It changes from completely green to IMO a reddish purple but the report says purple none the less.

the ring will only change when its moved very very close to the light. Then it changes completely purple.

Between these two stones, would one be considered more valuable in terms of color change being 1 changes completely and requires less light where as the other only completely changes when held very very close?

 

[Bron357]

Colour change in Alexandrites is usually expressed as a % change under specified light conditions. How much % of the whole gem changes colour.
For a lab report they use standardised specific light frequencies for assessment. These ”laboratory conditions” are hard to find in real life. Daylight conditions in the Northern Hemisphere in winter is quite different to daylight conditions in the Southern Hemisphere in summer and incandescent lighting conditions can vary depending on the light bulb you have (vs candle light).
Higher value is given to a purer green in daylight (vs yellowish green) and a clear purpleish red in incandescent (vs brownish purple)
Higher value is given to Alexandrites that change colour closest to 100% and change with an intensity, but these can be subjective.

 

[Bonsai]

the GIA lab report doesn't note intensity.

 

[LilAlex]

It's the "color temperature" of the light, not so much the type of light -- but the latter can be a shorthand for the type. In the shade on a cloudless day -- that's pretty cool light. My alex is the bluest there. The opposite extreme is candlelight or fireplace or a room lit only by old-school incandescent bulbs -- hard to find these days. My alex is vivid reddish-purple there. It has a report attesting to "strong" color change. However, it is more of a "fun" stone than a flat-out beautiful stone, unfortunately; in mixed lighting (where I live and work), it's mostly just dark.

Not sure what you mean by "how quickly they change." The effect is instantaneous -- but maybe you mean how close you need to be to the light source to see the effect.

So you want a strong color change and, as Bron357 writes, a complete (100%) color change. But even those are no guarantee that a stone is pretty. It's like a sapphire with a complete, straight-legged, well-aligned star with excellent and symmetrical movement -- but not a very pretty body color. On paper, it's hard to beat. In person, it's not a knock-out.

 

[Bonsai]

"" The effect is instantaneous -- but maybe you mean how close you need to be to the light source to see the effect."

Yes that's what I dont understand. Both stones completely totally change to purple. different shades of purple but its a complete change.
However 1 has to be much much closer to the bulb to change than the other. The other will change much farther away.

The reason I'm asking is so when I see other Alex stones described as "strong change" I will understand. The gia cert doesn't have any notes as to the intensity of the change on mine, though I'll assume it's strong since the entire color does change, just depending on how close to the light.

 

[LilAlex]

I'm guessing you're in mixed lighting and the proximity to the bulb just means a more complete change in the ambient light. If the stones are roughly the same tone and transparency, then I have no explanation.

 

[Bron357]

Do you have photos of them that shows what you are referring to?
I’m wondering if it’s due to body tone. I imagine that if the tone is deeper vs light, the colour change will “seem” more dramatic.
It’s a fine line I think, once the body tone tips into too dark they start looking murky.

 

[Bonsai]

No wasn't in mixed lighting.

I cant take photos b;c alexandrite doesn't photograph color accurately.

 

[Anne111]

I cant take photos b;c alexandrite doesn't photograph color accurately.

which is the main problem with such gems. Then there are the different type of light sources used, add photoshopping and the fact that in daily life you'll always have a mix of colors and you have many questionmarks ahead. The extreme day vs night colors are hardly ever seen, plus it's said that an alexandrite with 100% color-change is yet to be found. Probably the most difficult gem to buy on~or offline.