From: Carl Fransman (salto@salto.be)
Date: 04/06/00-02:40:18 AM Z
>Study of the clearing of Pt/Pd prints
>
>This study has documented some very significant findings concerning the
>clearing of Pt/Pd prints. This study makes use of the revised clearing
>test (in my Guide to Platinum Palladium Photographic Printmaking)
>involving the use of Potassium Ferricyanide as an indicator. Thanks to
>John Melanson for suggesting the use of this indicator.
>
>Several past observations have been made and verified and can be
>considered general trends concerning clearing.
>
>Most thin papers clear better and/or faster than thicker papers.
>
>POP type prints using Ammonium Ferric Oxalate sensitizer may clear in
>about half the time of DOP type prints using Ferric Oxalate sensitizer.
>This from previous work and not investigated further in this study.
>
>Prints made with a lower solution concentration of the coating
>ingredients will clear slightly faster. However, it must be remembered
>that a certain threshold concentration must be used to avoid weak
>prints. This from the Threshold Study.
>
>The most significant finding with this study is that an addition of
>Oxalic Acid and EDTA to the sensitizer solution dramatically reduces
>clearing times. (See the procedure and results below for details.)
>
>Only single agents were used for this study. It is suspected that a
>series of multiple agents might provide improved clearing, however the
>possibilities of combinations are numerous and may become a mute point
>at the conclusion of this study.
>
>
>CRITICAL CONSIDERATIONS:
>
>It is most important that the following be considered carefully as they
>can have a dramatic influence on clearing investigation. All relate to
>fogging.
>
>+ A safe light MUST be used. Work lights must be tested to assure that
>they will not fog the coating. Sodium vapor lights are an excellent
>choice.
>
>+ Coating brushes should be kept clean. Old sensitizer material can get
>into the print causing a fogging effect. Brushes should be rinsed well
>in distilled water and squeegeed dry with a paper towel after each use.
>Brushes should then be stored in a light tight box or bag.
>
>+ Fresh developer should be used. Developer that has been used for many
>prints may contain exposed material that will react with coatings
>causing a fogged appearance. This was a culprit in this study resulting
>in a lack of clearing in a reasonable time. When new developer was
>used, the repeated tests showed dramatically improved clearing. It
>should be routine practice to replace the developer rather than
>continuously replenish.
>
>+ Cross contamination can be a problem. The clearing indicator of a 10%
>solution of Potassium Ferricyanide proved to be far too sensitive.
>Uncoated samples were processed along with the other samples and
>although nothing could be detected without the indicator, the indicator
>would show some blue. Cross contamination is suspected to occur from
>used developer, rinse, clearing baths, and especially wash water. When
>samples were processed individually with fresh solutions and wash water,
>the false indications did not occur. However, it was not practical to
>process hundreds of samples with individual fresh baths and washes.
>Thus, a 1% solution of Potassium Ferricyanide was prepared and applied
>by smearing a little on with a clean, fresh Q-tip. (If a Q-tip with
>indicator solution touches an uncleared sample, it can produce false
>blue indications on a cleared sample. Also it is recommended to use a
>dropper to drop indicator solution onto the Q-tip, without touching. Do
>not dip the Q-tip into the solution. Also any trace of metal in the
>Potassium Ferricyanide solution may give a false blue color.)
>Evaluation was made relative to any indication on uncoated samples.
>This cross contamination is not critical for individual prints, but
>should be a consideration for producing archival prints. The final
>clearing bath and wash water should always be fresh. Also it must be
>remembered that the clearing indicator can be so sensitive as to give
>false indications and should be checked and referenced with a uncoated
>control.
>
>
>MATERIALS:
>
>One paper was used, Crane's paper (lot# 5302). This is a thick and
>traditionally long to clear paper (typically 40 to 60 minutes). Other
>papers may have different clearing times and/or respond to various
>clearing agents differently.
>
>Several clearing agents were tested. (water was 0.5 um filtered tap
>water)
>Code (used for this study); Agent; Description
>P; Phosphoric Acid (H3PO4); 2 ounces of 85% reagent grade per 1 gallon
>water
>C; Citric Acid; 20 grams per 1000 ml water (2% solution)
>S; Sodium Sulfide; 20 grams per 1000 ml water (2% solution)
>F; Sprint Fixer Remover; label directions (1 part plus 9 parts water)
>E; EDTA(Na4); 40 grams per 1000 ml water (4% solution)
>W: water; 0.5 um filtered tap water
>
>Note that HCl (Hydrochloric Acid) was not included because previous use
>has demonstrated that it can bleach the highlights of the print and
>mainly because I did not have any at the moment. However, the HCl may
>work fine (without bleaching) at the short clearing times this study
>demonstrates and should not be dismissed.
>
>Potassium Meta Bisulfite worked well but gave off too much sulphurous
>fumes so was eliminated from most of the tests and is not reported.
>
>Several Ferric Oxalate powders were investigated. However, results were
>a factor of the additives rather than the powder used. The Vizcay
>powder was selected as its composition and purity is best known. The
>addition of Oxalic Acid and EDTA made a significant difference. 3%
>Oxalic Acid was included because previous study indicated an advantage
>of having from 2% to 5% and I typically use 3%. 3% EDTA was selected
>being the same concentration as the Oxalic Acid. When used together, 1%
>EDTA was found to be adequate.
>
>Sensitizer Code; Description
>V; Vizcay Ferric Oxalate at 24% (Vizcay's preparation procedure is in my
>guide)
>VO; Vizcay Ferric Oxalate at 24% plus Oxalic Acid at 3%
>VE; Vizcay Ferric Oxalate at 24% plus EDTA at 3%
>VOE; Vizcay Ferric Oxalate at 24% plus 1% EDTA plus 3% Oxalic Acid
>
> (VOE = 24.00 g FO + 1.00 g EDTA + 3.00 g Oxalic Acid + H2O to make
>100 ml)
> Note: EDTA used was ethylene diamine tetra-acetic acid
> Synonyms: EDTA; Complexone II
> Molecular Formula: C10H16N2O8
> Molecular Weight: 292.25
> CAS: 60-00-4
> Purity Grade: pure
>(This was NOT the same EDTA(Na4) used as a clearing agent. The
>EDTA(Na4) tested for clearing was some sent to me by John Melanson.
>John may have more info as to the source.)
>
>The metal salt solutions were K2PdCl4 (16.2%) and K2PtCl4 (20.6%) in a
>ratio of 5 parts Pd and 2 parts Pt. The strengths of these solutions is
>that calculated to work with the 24% FO sensitizer strength.
>
>
>PROCESSING:
>
>All samples were processed as follows:
>coating solution mixed
>brush coated (with coating edge indicated and as instructed in my guide)
>dried
>identified with marks and then cut into samples
>1 minute in Potassium Oxalate (developer and all baths at ambient
>temperature)
>2 minutes in water
># minutes in clearing agent
>5 minute wash in water
>dried
>evaluated
>Potassium Ferricyanide (1% solution) applied (smeared on with clean
>Q-tip) to part of coated area
>exposed for 12 minutes with UV lamps (about double typical printing
>time)
>10 minute wash to remove all yellow from Potassium Ferricyanide
>dried
>evaluated
>
>NOTE: If one uses a different developer or different conditions, those
>should be used for the test.
>
>
>IDENTIFICATION & NOMENCLATURE:
>Samples are referred to as X# where
>X = the code letter of the clearing agent
># = number of minutes in the clearing agent
>
>Observations of the evaluations are coded as follows:
>For areas without Potassium Ferricyanide:
>x = no sample
>0 = identical to uncoated paper
>1 = very faint gray color (the slightest distinction)
>2 = light gray color
>3 = gray color
>4 = light brown or light yellow-brown color (may include gray)
>5 = brown or deep yellow-brown color (similar to coating color)
>For areas with Potassium Ferricyanide:
>no code = no change
>a = faint blue color
>b = blue color
>
>Note: Consideration should be given for unnecessary cross contamination
>and any "0a" rated samples might be considered completely clear.
>
>For example:
>3b - means the coated area was a gray color and the area with Potassium
>Ferricyanide was a blue color.
>1 - means the coated area was only a very faint gray color and the area
>with Potassium Ferricyanide showed no change.
>
>
>OBSERVATIONS:
>samples = observations
>
>For V sensitizer (FO only):
>
>P5, P10, P20, P30, P40 = 5b, 4b, 3b, 2b, 1a
>C5, C10, C20, C30, C40 = 5b, 4b, 3b, 1b, 1b
>S5, S10, S20, S30, S40 = 5b, 4b, 3b, 2b, 1a
>F5, F10, F20, F30, F40 = 2b, 1b, 1a, 0a, 0a
>E5, E10, E20, E30, E40 = 4b, 3a, 2a, 2, 2
>W5, W10, W20, W30, W40 = 5b, 5b, 4b, 4b, 4b
>
>
>For VO sensitizer (FO + OA):
>
>P5, P10, P20, P30, P40 = 2b, 1b, 1b, 1b, 1a
>C5, C10, C20, C30, C40 = 1b, 1b, 1a, 1a, 0a
>S5, S10, S20, S30, S40 = 2b, 2b, 1b, 1b, 1a
>F5, F10, F20, F30, F40 = 1b, 1b, 0, 0, 0
>E5, E10, E20, E30, E40 = 1a, 1a, 1a, 0, 0
>W5, W10, W20, W30, W40 = 3b, 1b, 1b, 0b, 0b
>
>
>For VE sensitizer (FO + EDTA): (Note change in times)
>
>P5, P10, P15, P20, P30 = 1a, 1a, 1, 0, 0
>C5, C10, C15, C20, C30 = 1a, 1, 1, 0, 0
>S5, S10, S15, S20, S30 = x, x, x, 1a, 0
>F5, F10, F15, F20, F30 = 1a, 1a, 0, 0, 0
>E5, E10, E15, E20, E30 = 1a, 0a, 0, 0, 0
>W5, W10, W15, W20, W30 = x, 1b, x, x, 1a
>
>
>For VOE sensitizer (FO + OA + EDTA): (again note change in times)
>
>P5, P10, P15, P20 = 0a, 0a, 0a, 0a
>C5, C10, C15, C20 = 0a, 0a, 0a, 0a
>S5, S10, S15, S20 = 0a, 0a, 0a, 0
>F5, F10, F15, F20 = 0a, 0a, 0, 0
>E5, E10, E15, E20 = 0a, 0a, 0, 0
>W5, W10, W15, W20 = 1b, 1b, 0b, 0a
>
>
>For comparison, with old developer, VOE gave the following results:
>
>P5, P10, P15, P20, P30 = 2b, 2a, 2a, 2a, 1a
>C5, C10, C15, C20, C30 = 2b, 2b, 2a, 1a, 1a
>S5, S10, S15, S20, S30 = 2b, 2b, 1a, 1a, 1a
>F5, F10, F15, F20, F30 = 2, 2, 1, 1, 1
>E5, E10, E15, E20, E30 = 2, 2, 2, 2, 1
>W5, W10, W15, W20, W30 = 2a, 2a, 2a, 2, 2
>
>
>
>CONCLUSIONS:
>
>The addition of either Oxalic Acid or EDTA to the Ferric Oxalate (FO)
>sensitizer solution improved clearing and reduced clearing times.
>
>Best results were obtained when both Oxalic Acid and EDTA were added.
>Note that even water (without any clearing agent) cleared completely in
>20 minutes plus rinse and wash when both Oxalic Acid and EDTA were
>added.
>
>A used developer will dramatically hinder clearing.
>
>The choice of sensitizer additive and a fresh developer is more
>important to good clearing than the choice of clearing agent.
>
>
>RECOMMENDATIONS:
>
>For proper clearing of Pt/Pd prints it is recommended that Oxalic Acid
>(3%) and EDTA (1%) be added to the Ferric Oxalate sensitizer solution.
>Note that previous and ongoing work from the Threshold Study has shown
>the addition of up to 5% of Oxalic Acid and up to 3% EDTA to the
>sensitizer does not seem to degrade the quality of the print.
>
>Since Potassium Meta Bisulfite produces a strong sulphurous odor
>(especially when used in an open tray), it is NOT recommended.
>
>Sprint Fixer Remover is a good choice for the selected paper as it
>provided the best and fastest clearing in every case. A different paper
>may favor another clearing agent.
>
>A wash time of 10 minutes with at least one change of fresh water is
>recommended.
>
>The recommended times for clearing the selected paper are:
>10-15 minutes for the Sprint Fixer Remover or EDTA(Na4) giving a total
>processing (develop through wash) time of 23-28 minutes.
>15-20 minutes for Sodium Sulfide giving a total processing (develop
>through wash) time of 28-33 minutes.
>20 minutes for Phosphoric Acid or Citric Acid giving a total processing
>(develop through wash) time of 33 minutes.
>
>It should be routine practice to replace the developer rather than
>continuously replenish.
>
>
>Have a clear day.
>
>--
>Jeffrey D. Mathias
>http://home.att.net/~jeffrey.d.mathias/
>
Jeffrey,
once more, you prove that science and practice are the basis of good
things.
Congrats with your in depth work!
Carl
______________________
SALTO
Printing & Lithography
Groenplaats 1
3621 Rekem-Lanaken
BELGIUM
tel +32 89 71 87 90
fax +32 89 73 18 30
salto@salto.be
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