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Recertification of Neutral Density Standard Reference Materials for Regular Spectral Transmittance


The certification for all SRM neutral density filters expires after two years. We maintain a program to recertify such filters produced by us. Filters returned for recertification are measured in the "as received" condition, taken apart and carefully cleaned, and then a final recertification measurement is made. The filters are returned to the customer with a "Report of Recertification" that serves as a replacement for the original certificate. The report contains the "as received" data as well as the new certification data, to permit the customer to evaluate the performance of the filters during the prior certification period.


Photograph of four filters in black anodized metal cuvette holders, with a labeled metal case and lid.

SRM 2031c  Metal-on-Fused-Silica Neutral Density Filters

Credit: Lane Sander
  • Certifications and recertifications for SRMs 930x, 1930, 2930, and 2031x expire after two years. 
  • To have a filter set recertified, go to or go to, click on ‘Shop’ in the upper right corner, then click on ‘Calibration Services’. Follow the instructions on the website to login to an existing account or create a new account.
  • SKU number for recertification of SRMs 930x, 1930, and 2930 is 38065C. SKU number for recertification of 2031x is 38066C.
  • Provide your return method of shipment (UPS, FedEx) with account number. Do not provide a prepaid return shipping label.
  • Required information: Company Name, Shipping Address, Billing Address, Filter Type (for example, SRM 930d), Filter Set Number (for example, set 311), the taxpayer identification number (TIN, for U.S. customers only), and a Contact Name with E-mail Address and/or Phone Number.
  • If you are paying by purchase order, then in addition to the information above, we require the P.O. number and the value of the P.O. in U.S. dollars.
  • Prepayment required for international orders.
  • Please include either the order confirmation number (O-XXXXXXXXXX) or a copy of the purchase order in the box so that the order can be easily identified.

For help or questions, contact Iftikhar.awan [at] (Iftikhar[dot]awan[at]nist[dot]gov) and/or peter.trask [at]

Send your filters to:

NIST 100 Bureau Drive
Building 301, Receiving
Gaithersburg, MD 20899

Attention: 227/A111 Optical Filters Program


  1. Mavrodineanu, R., An Accurate Spectrophotometer for Measuring the Transmittance of Solid and Liquid Materials, NBS Journal of Research 76A, No. 5, pp. 405-425, (1972).
  2. SP 260-81 - Accuracy in Analytical Spectrophotometry, pp. 46 - 66.
  3. J. C. Travis, M. V. Smith, S. J. Choquette, and Hung-kung Liu, "Certified Transmittance Density Uncertainties for Standard Reference Materials using a Transfer Spectrophotometer," NIST Technical Note 1715, (2011). 
Created November 24, 2009, Updated November 6, 2023