I mixed items sold as henna powders with lemon juice and left them 20 minutes, then put them between microscope slides and photographed them at 60x.  These slides show henna powders' comparitive particle size, and whether they have debris, other plant material,  and dye.  Rubbing the two microscope slides together made a gritting sound if there was sand or mineral debris in the henna.

Here's what you should know before you look at the pictures:

Particle size doesn't have anything whatsoever to do with stain results.
These pictures will only tell you whether henna has dye, grit, or chunks in it.

Particle size:
This is a #3 pencil lead at 60x, the same magnification as the slides.   If you use a #3 metal tip, all particles MUST be smaller than this lead is wide, or the henna will clog your tip, and you'll either have to sift the henna or pick out the clog.  On my screen, this lead is about the size of my finger.  If any chunk in a picture is as large as my finger is wide, it's not going through a #3 tip. 

Many henna powders have particles larger than this lead. If you look at the microscopic pictures of the powder, you'll see if you're getting henna you'll have to sift, like this one:

Sifting:
If you like the results of a henna that's "chunky", you can sift it through a Fred-O-Matic, and the clogging problem is solved.  See: Mr. Chunky makes friends with Fred http://www.sphosting.com/reverndbunny/frednchunky.html

DYE:
Many suppliers, especially in India, add green dye to their henna to make it appear "better". 
A bright green henna color may indicate dye has been added to the powder, and has nothing to do with the stain result.

The vivid green chunks  here, spreading green are artificial green dye, coal tar dye, added to make the product more "eye-appealing".  The presence of green dye is irrelevant to the stain. The presence of this dye and is confirmed and identified in: 

"Study of Quality Characteristics of Henna", Chourasia, Sardar, Patil, Mathew,Kanpur, India: Essential Oil Association of India, 1989

"Major contaminants /adulterants in henna leaves are stems, dirt, plant waste and other leaves. However in case of henna powder admixture of dyed sand is observed. It shas been reported that for adulteration, finely ground local sand is used. It is first dyed with auramine yellow (C.I. No. 41000) and then green with diamond green (C.I. No. 20440). This is then mixed with pure henna powder. The extent of adulteraion is viariable in accordance with the price of the powder reflected therein.

"Added azo dyes were not found in henna leaf samples, but yellow and green coal tar dyes were observed in powdered samples. As mentioned earlier, this may be due to the presence of (the afore mentioned dyed sand). Unlike Lawsone, the natural color of henna, these added synthetic azo-dyes used for dyeing the sand or for polishing the leaves may have an adverse effect on the skin. It is, therefore, necessary to ensure that these artificial dyes are not there in the product marketed.

Virtually all henna powders from India that I have surveyed have this dye!

Other Dye Plants Added to Henna:

The deep red pieces in this picture are Myrobalan, a dye plant: 

Myrobalan \My*rob"a*lan\ (?), Myrobolan \My*rob"o*lan\ (?), ] n. [L. myrobalanum the fruit of a palm tree from which a balsam was made.  A dried astringent fruit much resembling a prune. It contains tannin, and was formerly used in medicine, but is now chiefly used in tanning and dyeing. Myrobolans are produced by various species of Terminalia of the East Indies, and of Spondias of South America.
  -- web1913
Some of these added dye plants give a redder henna color, and are harmless, but they are NOT henna, and the exporters frequently do NOT admit they have adulterated their henna with another dye plant.
 

The round clear spheres are air bubbles trapped between microscope slides. Ignore them.

Grit:
Many henna powders have mineral grit, sand, and dirt in them.  I rub the henna paste between two microscope slides, and if I hear a gritting sound, there's dirt, sand or grit in the henna.  If I don't hear anything, the henna is clean.  Grit doesn't change the henna stain, but if there's a lot of it, you're paying for dirt rather than henna.
 

Henna powders viewed through a microscope at 60x:

For comparison: home grown henna, known to be absolutely pure: http://www.sphosting.com/reverndbunny/homegrown.html

Afshan:
http://www.sphosting.com/reverndbunny/Afshan.html

Al Henna
http://www.sphosting.com/reverndbunny/AlHenna.html

Amazing Body Art Supply "black henna"
http://www.sphosting.com/reverndbunny/Amazing.html

Art With Love
http://www.sphosting.com/reverndbunny/ArtLove.html

Ayur, August 2002
http://www.sphosting.com/reverndbunny/Ayur.html

Ayur sample B, September 2002 
http://www.sphosting.com/reverndbunny/Ayur 2.html

Bina 
http://www.sphosting.com/reverndbunny/Bina.html

Black Henna
http://www.sphosting.com/reverndbunny/Blackhenna.html

Black Rose Kali Mehandi "black henna:
http://www.sphosting.com/reverndbunny/Kali.html

Beauty Henna "Black Henna"
http://www.sphosting.com/reverndbunny/Beautyblack.html

Divya Summer 2000
http://www.sphosting.com/reverndbunny/Divya.html

Divya Black Henna Summer 2000
http://www.sphosting.com/reverndbunny/DivyaBlack.html

Dulhan Spring 2002 New York
http://www.sphosting.com/reverndbunny/Dulhan.html

Dulhan September 2002 Detroit 
http://www.sphosting.com/reverndbunny/DulhanDetroit.html

Five Fives 
http://www.sphosting.com/reverndbunny/FiveFives.html

Frontier Henna
http://www.sphosting.com/reverndbunny/Frontier.html

Indigo
http://www.sphosting.com/reverndbunny/Indigo.html

Hana Atabake
http://www.sphosting.com/reverndbunny/AtabakiIran.html

HennaWorks henna powder Summer 2001
http://www.sphosting.com/reverndbunny/Hennnaworks.html

Harazi July 2002
http://www.sphosting.com/reverndbunny/Harazi.html

Hasina September 2002
http://www.sphosting.com/reverndbunny/hasina.html

Jamila (body art quality) Summer 2002
http://www.sphosting.com/reverndbunny/Jamila.html

Jamila (hair quality) summer 2002
http://www.sphosting.com/reverndbunny/Jamilahair.html

Jani Henna, Summer 2001 
http://www.sphosting.com/reverndbunny/Jani.html

J B and Co. Summer 2002
http://www.sphosting.com/reverndbunny/JB.html

Kenzi Sping 2002 
http://www.sphosting.com/reverndbunny/Kenzi.html

Kenzi Summer 2002
http://www.sphosting.com/reverndbunny/Kenzisummer.html

Kimia 2001
http://www.sphosting.com/reverndbunny/Kimia2001.html

Kimia, August 2002 
http://www.sphosting.com/reverndbunny/Kimia.html

Kina: August 2001
http://www.sphosting.com/reverndbunny/Kina.html

LifeArt Henna Powder  from Mehndi Mud Spring 2001: 
http://www.sphosting.com/reverndbunny/Lifeart.html

Mangal
http://www.sphosting.com/reverndbunny/mangal.html

Mazaya, August 2002 
http://www.sphosting.com/reverndbunny/Mazaya.html

Mazaya, October 2002
http://www.sphosting.com/reverndbunny/Mazayafall2002.html

Mughleazam
http://www.sphosting.com/reverndbunny/Mughleazam.html

Mumtaz al_Aroosa, September 2002 
http://www.sphosting.com/reverndbunny/Mumtaz.html

Mumtaz al Aroosa, October 2002
http://www.sphosting.com/reverndbunny/MumtazDetroit.html

Navaid 1 August 2002
http://www.sphosting.com/reverndbunny/Navaid1.html

Navaid Sarah  sample 1, Spring 2002 
http://www.sphosting.com/reverndbunny/NavaidSarah.html

Navaid Sarah, sample 2, Fall 2002
http://www.sphosting.com/reverndbunny/NavaidSarah2.html

Mystery Henna Summer 2002 
http://www.sphosting.com/reverndbunny/Mystery.html

ONS Henna September 2002
http://www.sphosting.com/reverndbunny/ONS.html

Persian Red Summer 2002
http://www.sphosting.com/reverndbunny/Persianred.html

Raachni Henna: 
http://www.sphosting.com/reverndbunny/Raachni.html

Radico 2001
http://www.sphosting.com/reverndbunny/Radico2001.html

Radico 2002
http://www.sphosting.com/reverndbunny/Radico2002.html

Sahara Tazarine 
http://www.sphosting.com/reverndbunny/Tazarine.html

Sharkiyya 2001
http://www.sphosting.com/reverndbunny/Sharkiyya2001.html

Sharkiyya October 2002
http://www.sphosting.com/reverndbunny/Sharkiyyafall2002.html

Shelly September 2002
http://www.sphosting.com/reverndbunny/Shelly.html

Shihri July 2002
http://www.sphosting.com/reverndbunny/Shihri.html

Shihri October 2002
http://www.sphosting.com/reverndbunny/ShihriOct.html

TaziiAugust 2002
August 2002  http://www.sphosting.com/reverndbunny/Tazii.html

Usha August 2002,
August 2002  http://www.sphosting.com/reverndbunny/Usha.html

Zarqua Black Henna 
http://www.sphosting.com/reverndbunny/Zarqua.html

Zubeda
http://www.sphosting.com/reverndbunny/Zubeda.html

If you think databasing microscopic pictures of henna is a good idea, so everyone can learn more about henna marketing patterns, geography, improvements in quality over time, deterioration in quality, adulteration, purity, weather effect, geographic factors, ethnic preferences ... PLEASE send me samples of henna YOU have!  The more complete a database is, the more useful it is. 

I'd love to have a complete record of henna going back to at least 1995, when henna started to become popular world wide.  We can all learn so much from this, and perhaps make henna better for everyone.

Please send henna samples to:
Catherine Cartwright Jones
4237 Klein Ave.
Stow, Ohio, 44224
USA

It is preferable to have unopened packages.
In lieu of that, please take a clean spoon, take a henna sample from the middle of your henna, and put it into a clean ziplock bag.  Please label the bag as to 
1) where did you get it?
2) when did you get it?
3) brand name?
4) country of origin?

Henna artists and researchers will thank you!  Before this, there was NO public database with microscopic pictures of henna.  Help make this database grow so everyone can learn more about henna!