Recently whilst researching Calotypes and Calotypists in my home county of Surrey I came across a photographer called Henry D Taylor who apparently learned the process from Samuel Buckle the inventor of the Buckle Brush and a successful Calotypist in his own right . Buckle specialised in the Calotype up  to 1857 when he turned to the wet plate Collodion process to make his pictures. He was probably one of the few to actually make a living from the Calotype. I particularly like  his Tondo images.He died in 1860. My interest was further piqued by the words "Buckle remained loyal to Talbot's process" which echo those of a certain B B Turner.

Buckles process can be found here in De Abneys instructions of photography of 1884. The instructions are simple but thorough

More information on Buckle can be found here

Buckles process isnt Talbots , probably by the mid 1850s any Calotype made by the English pre silvered method could be refered to as Talbots process. His method of producing Double Iodide of silver differs slightly to most of his contemporaries.

Talbots instructions for producing the Iodized paper were vague. Broadly speaking he brushed a good quality writing paper with a 7.5% solution of silver nitrate. This was allowed to surface dry. It was then dipped in a bath of 5.6% of potassium nitrate. After which it was  washed and dried. If properly prepared this was not light senstive and could be stored until required ,  the sensitizing solution was then applied. His vague instructions together with  varying paper quality and inconsistent chemical quality meant failure for many early photographers resulting in many turning away from the Calotype. The purpose of this was of course to create the exquisitely sensitive (in comparison to what had gone before) Silver Iodide.

It was the DublinerWilliam Holland Furlong who first simplified Talbot's iodizing process  in 1843 at the age of 17 ! He was based in the town of St Andrews in Scotand at the time .Adamson hints that his method came from Furlong 
South of the border the English Calotypists struggled with the double wash method until the 1850s when they came up with their own slightly more convoluted method of a single wash method of Iodization. Detailed by Dr Diamond in 1853 this involves equal amounts of silver nitrate and potassium iodide in a small amount of water to produce silver iodide with the potassium nitrate being poured off before more water is added and poured away. Yet more water is added with Potassium Iodide added bit by bit until as if by magic the Solution clears and is said to in perfect balance and ready to be applied to the paper. The paper is then rinsed again ! All very time consuming indeed it can take all day during the dark winter months..In Photographic notes vol 1 1856 Furlong says that " I have never found the slightest advantage in first precipitating the Iodide of Silver and then washing it ".
Sutton fine tunes his double Iodide of silver adding even more complication  , Chas Longs is similar but without the fine tuning adding Potassium Iodide to the silver iodide until it clears, and Adamson's process achieves the same results in a far simpler and easier method by just adding potasium Iodide to a small amount of silver nitrate dissolved in distilled water until it clears. In all of the above the solution clears , if you have tried it , it is always a bit of a relief when it does ! I thought that the chemicals were in perfect balance when the solution clears but in Buckles process he states that the solution is ready when it becomes "just not clear but semi translucent" 

So now I am wondering about the science behind producing Double Iodide of silver. I can see all of its advantages if you get it right the Calotypes are extraordinary plus it uses less chemicals then continental methods which require much stronger sensitisers. The Iodized paper lasts well and has the further advantage that it can be sunned (exposed to the sun for ten minutes prior to sensitization) to enhance contrast an idea that Furlong attributes to Dr John Adamson.

Why is it called double iodide ? I found the answer in the journal of the photographic society Nov 21 1856 page 152
When iodide of silver is dissolved in a strong solution of Iodide if Potassium a salt is formed known as double Iodide of Potassium and Silver. Which would crystallize out if the solution evaporated. But in dilution with water it is decomposed again into free Iodide of Potassium which remains dissolved and insoluble Iodide if silver which is precipitated in the surface of the paper.

 Seemingly the English method of producing Double Iodide was invented by a gentleman called C J Jordan he wrote a piece called Preparation of Iodized Papers by One Solution Only in 1848.This was printed in the Mechanics magaziine and the pharmaceutical times . He appears to have been a chemist, but apart from that his full name and place of residence are unknown and none of his photography appears to have survived. I have read this article which was subsequently reprinted in 1855 in the Journal of the photographic society and it doesnt really detail the process it just gives a general idea of his process. He is described as " One of the oldest friends of photography" and I can only assume that he demonstrated the process to Dr Diamond .

Personally I prefer Furlongs method and I still marvel every time the solution clears.
Furlong was one of the disciples of light at St Andrews in the early 1840s , starting out as assistant to Arthur Connell professor of chemistry in 1841and his method of producing Double of Iodide of silver was pivotal in the success of Hill and Adamson. There are a couple of Calotypes of St Andrews by Furlong in the Brewster Album as well one taken in 1842/43 by John Adamson of Furlong and Robert Adamson standing on a wooden bridge . 
The five characters in the above paragraph were real pioneers in the Calotype. What amazes me is that somehow Furlongs method of Iodisation didn't reach England. Potassium Iodide cost a fortune back then and Furlongs method would have cost about the same as Talbots and was cheaper than the English method.. Talbot was in contact with St Andrew's , he was great friends with Brewster who also knew Furlong ,could they have kept it secret ? Indeed Furlong even corresponded with Talbot - the plot thickens ! 
Furlong disappeared from St Andrew's in the 1840s returning to his home in Ireland. He must have kept abreast of news and developments as he resurfaced in 1856 as Furlonge  to refute Jordan's claim to being the first to simplify Talbot's Iodising process.
As William Holland Furlonge wrote in 1856 next to the possession of good paper the proper performance of the Iodizing process is by far the most essential to the success of the Calotype.
Furlong along with Hill and Adamson revolutionised the Calotype in the early 1840s, Hill with his eye for composition, Adamson with his technical ability and Furlong with his chemical wizardry . Hill and Adamson's photographs are rarely surpassed even today.
Furlongs Iodizer is as follows. In John Adamson's words "25 grains of nitrate of silver are dissolved in one ounce of distilled water, to which 3 1/2 drachms of Iodide of potassium is then added and shaken until the copious yellow precipitate is dissolved. This solution is to be freely brushed over the marked side of the paper by a lean and dry camel-hair pencil or with a little cotton wool." The paper is allowed to dry and is then washed to leave Iodide of silver.
Talbot's method should be produced in the dark room, the double iodide in subdued light though I tend to use the dark room to eliminate any doubts.

I recently had a couple of Calotypes where the paper didn't appear to sensitise properly there where big white patches , I put this down to me not applying the sensitiser properly but I now think it was that the Iodized papers wern't washed thoroughly and potassium nitrate was still present. And even if a tiny amount of silver nitrate is still present then the paper blackens.

Washing methods vary widely in the manuals of the day. From a couple of rinses by Chas Long to 24 hours by Thomas Sutton.
What I have learnt through experimentation is  that 4 hours washing under running water is good and that you shouldn't attempt to wash too many papers in one go. 8 hours immersion is fine too. Placing one or two sheets in individual trays and changing the water regularly works well .Anything less than 4 hours can sometimes result in some Calotypes exhibiting big white blotches.

The difference in the resulting Calotypes between  Furlongs and the English method seems to be minimal . Both processes produced a nice primrose coloured paper with any variation in hue imperceptible to my eye. Buckles process did cause more of a mess in the wash water after developing. The first bath being almost brown when I turned the lights on.To my eye Adamson's / Furlongs method produces the more Vibrant Calotype.
Potassium Iodide in 1849 was 3 shillings an ounce , the same sum would have bought a quarter of a ton of coal ! Failure was expensive.

Make sure you buy your chemicals from a reputable source to eliminate any doubts .

Lastly cleanliness is godliness when it comes to the Calotype make sure every thing is spotless , eyedroppers ,syringes, bottles everything ! Change them if need be. How our ancestors produced such works of art still leaves me in awe.

I have collated the various Iodising methods that I have found in the manuals and journals of the 1840s and 1850s . This of course relates to the English Calotype or Talbotype as it was sometimes known . They are all related to Talbots original process. The proper Iodisation of the paper was key to the success of the Calotype as indeed was the actual paper. Time and time again you read about early practitioners from England , Scotland and America struggling with the process and this was largely due to a rather vague Iodisation process.
The double Iodide method proved to be a far more exact and reliable method of producing good iodised paper than Talbot's original method . It works today in the 21stCentury. The watershed seems to be 1853 and Dr Diamonds paper combined with Talbots withdrawal of his patent in 1854 .
Of course the Gallic acid in the sensitiser also caused problems and only Adamson excludes it , but that is another story. (dios = double iodide of potassium and silver).

Arthur Kerr    double wash    1853    Anthony's photographic album 1889    as taught by Samuel  Buckle.                               
Brewster    double wash    1843    Edinburgh review    
Brodie    double wash        Willats 1847-1852    
Henry D Taylor    double wash    1853    Anthony's photographic album 1889    taught by Arthur Kerr
Llewellen    double wash    1856    Sparling    
Mr Hazel    double wash        Willats 1847-1852    
Robert Bingham    double wash    1851    The photographic art jounal    
A successful practicioner    double wash         Willats 1847-1852    Willats ?
Cundell    Double wash    1844    The Philosophical magazine & Hunt 1853    
Samuel Buckle    double wash    1853    Anthony's photographic album 1889    
WH Furlonge    single wash dios    1844    paper read by John Adamson in 1843 to the literary and philosophical society of St Andrews.    
Chas long    single wash precipitated dios    1854    practical photography on glass and paper    
Dr Diamond    single wash precipitated dios    1853    notes and queries also Sparling 1856    
Henneman    single wash precipitated dios      pre 1855    cynan    
Henry D Taylor    single wash precipitated dios    post 1853    Anthony's photographic album 1889    
J B Hockins    single wash precipitated dios    1860    practical photography on glass and paper    
Joachim Otte    single wash precipitated dios    1858    Landscape photography    
Jordan CJ    single wash dios    1848    preparation of Iodized papers by one solution only . pharmaceutical times August 5 1848.    
Negretti    single wash precipitated dios    1864    copied from Chas longs manual    they bought Bland and Longs premises at Fleet St
Samuel Buckle    single wash precipitated dios     post 1853    D Abbey 1884    
Thomas Sutton    Single wash precipitated dios    1855    The Calotype process a hand book    
W H Burbank    Single wash precipitated dios    1888    The photographic negative described as Talbot's process .
WHT    (Thornthwaite)Triple wash    1843    Photographic manipulation    improvements credited to Mr Mitchell and Dr Ryan . Washed with potassium Iodide , then silver nitrate and dipped in potassium iodide.
Finally using this time line I have to retract an earlier thought of mine , namely that B B Turner hadn't used Talbots process but one of the later variations. But looking at it this is not the case . He first started making his Ultra large Calotypes in 1851 to 1852 at the end of the Great exhibition . And his Album "Photographic Views from  Nature " taken in 1852 , 1853 and 1854 on paper by Mr Fox Talbot's process . In which case they are truly remarkable . B B Turner kept a scrap book of articles from the journals of the day detailing various methods that interested him. I need to track this down and read this !

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